Devices and methods for treating medical disorders with evoked potentials and vagus nerve stimulation

ABSTRACT

Devices, systems and methods for treating medical disorders, such as migraine or other primary headaches, or fibromyalgia, by noninvasive electrical stimulation of a vagus nerve, used in conjunction with the measurement of evoked potentials (EPs). The system comprises a stimulator that is applied to the surface of the patient&#39;s neck to apply electrical impulses sufficient to stimulate a cervical vagus nerve, scalp electrodes that are used to measure EPs that are evoked by that stimulation, feedback or biofeedback circuits to vary the stimulation based upon EP characteristics, and other sensory stimulation modalities that produce EPs. The system is preferably used to optimize the placement of the stimulator, to test whether a patient is a suitable candidate for treatment using vagus nerve stimulation, and to select the stimulation parameters that optimized acute or chronic treatment, e.g., by correcting an EP habituation deficit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 14/212,992filed 14 Mar. 2014; which is a Continuation in Part of U.S. applicationSer. No. 13/872,116 filed 28 Apr. 2013; each of which is herein fullyincorporated by reference for all purposes.

BACKGROUND

The field of the present invention relates to the delivery of energyimpulses (and/or energy fields) to bodily tissues for therapeuticpurposes. The invention relates more specifically to the use ofnon-invasive or minimally-invasive electrical stimulation of the vagusnerve in a patient's neck in order to treat various medical disorders,such as primary headache (e.g., migraine) or fibromyalgia.

Migraine headache is a type of primary headache, i.e., a headache thatdoes not occur secondarily to another cause. Migraine is a highlydisabling disorder, with an annual prevalence of 6-9% among men and15-17% among women. Approximately 20-30% of migraine sufferers(migraineurs) experience an aura, ordinarily a visual aura. The auratypically lasts for 5 minutes to an hour, during which time the patientexperiences sensations such as moving zig-zag flashes of light, blindspots or tingling in the hand or face. The migraine headache typicallypasses through the following stages: prodrome, aura, headache pain, andpostdrome. All these phases do not necessarily occur, and there is notnecessarily a distinct onset or end of each stage, with the possibleexception of the aura. An interictal period follows the postdrome,unless the postdrome of one migraine attack overlaps the prodrome of thenext migraine attack. The pain is often reported as starting in theoccipital/neck regions, later becoming frontotemporal. It is throbbingand aggravated by physical effort [Bert B. VARGAS, David W. Dodick. TheFace of Chronic Migraine: Epidemiology, Demographics, and TreatmentStrategies. Neurol Clin 27 (2009) 467-479; Peter J. GOADSBY, Richard B.Lipton, Michel D. Ferrari. Migraine—Current understanding and treatment.N Engl J Med 346 (4, 2002): 257-270; Stephen D SILBERSTEIN. Migraine.LANCET 363 (2004):381-391].

Signs of sensory hyper-excitability often make their debut during thepremonitory or prodromal phase of a migraine headache, which lateraccompany the headache phase. The hypersensitivity to external stimulimay manifest itself as photophobia, phonophobia, hyperosmia andcutaneous allodynia, corresponding respectively to heightenedsensitivity to light, sound, odor, and touch (particularly of the scalpand face). Therefore, migraineurs often seek a dark, quiet place duringthe attack. In the interictal period between attacks, migraineurs alsoshow abnormal processing of sensory information that is apparently dueto dysfunctional regulation of cortical excitability [COPPOLA G,Pierelli F, Schoenen J. Is the cerebral cortex hyperexcitable orhyperresponsive in migraine? Cephalalgia 27(2007):1427-1439; AURORA S K,Wilkinson F. The brain is hyperexcitable in migraine. Cephalalgia27(2007):1442-1445; COPPOLA G, Schoenen J. Cortical excitability inchronic migraine. Curr Pain Headache Rep 16(2012):93-100; MAGIS D,Vigano A, Sava S, d'Elia T S, Schoenen J, Coppola G. Pearls andpitfalls: electrophysiology for primary headaches. Cephalalgia33(8,2013):526-539].

Pharmacological administration of triptans is currently the mosteffective treatment for acute migraine headaches (Sumatriptan,Zolmitriptan, Naratriptan, Rizatriptan, Eletriptan, Almotriptan, andFrovatriptan). However, only 30-40% of migraineurs are pain-free twohours after the administration of triptans. Of those who do respond, onein three will experience a migraine recurrence within 24 hours.Furthermore, because triptans constrict cranial blood vessels throughactivation of serotonin 5-HT1B receptors, as a side effect they may alsocause vasoconstriction of coronary vessels. Switching to a differenttriptan might benefit some non-responders, but for many suchmigraineurs, non-migraine-specific rescue drugs that have significantside effects may be the last and potentially ineffective option(opioids, neuroleptics, and/or corticosteroids). Accordingly, migrainetreatment methods are needed that are more effective than triptanpharmaceuticals but that do not exhibit significant side effects.Furthermore, more effective treatment methods are needed to reduce thelikelihood that a migraine attack will occur [Stephen D Silberstein.Migraine. Lancet 363 (2004):381-391; Peter J GOADSBY, Till Sprenger.Current practice and future directions in the prevention and acutemanagement of migraine. Lancet Neurol 9(2010): 285-98; Joel R. SAPER,Alvin E. Lake III, Philip A. Bain, et al. A Practice Guide forContinuous Opioid Therapy for Refractory Daily Headache: PatientSelection, Physician Requirements, and Treatment Monitoring. Headache50(2010): 1175-1193].

Non-pharmacological treatments of migraine headaches have a longhistory, as an alternative or complement to treatment with drugs. Suchnon-parmacological treatments include behavioral therapy, physicaltreatments such as massage, phototherapy, acupuncture, greater occipitalnerve blockade and trigger point injections, electrical stimulation withimplanted electrodes in lieu of occipital or auriculotemporal nerveblockade, magnetic stimulation just below the occipital bone, andsurgery [Peter J. KOEHLER and Christopher J. Boes. A history of non-drugtreatment in headache, particularly migraine. Brain 133(2010):2489-2500].

Another non-pharmacological treatment that is particularly relevant tothe present invention is the electrical stimulation of the migraineur'svagus nerve. Vagus nerve stimulation (VNS) was developed initially forthe treatment of partial onset epilepsy and was subsequently developedfor the treatment of depression and other disorders. The left vagusnerve is ordinarily stimulated at a location within the neck by firstimplanting an electrode about the vagus nerve during open neck surgeryand by then connecting the electrode to an electrical stimulator circuit(a pulse generator). The pulse generator is ordinarily implantedsubcutaneously within a pocket that is created at some distance from theelectrode, which is usually in the left infraclavicular region of thechest. A lead is then tunneled subcutaneously to connect the electrodeassembly and pulse generator. The patient's stimulation protocol is thenprogrammed using a device (a programmer) that communicates with thepulse generator, with the objective of selecting electrical stimulationparameters that best treat the patient's condition (pulse frequency,stimulation amplitude, pulse width, etc.) [U.S. Pat. No. 4,702,254entitled Neurocybernetic prosthesis, to ZABARA; U.S. Pat. No. 6,341,236entitled Vagal nerve stimulation techniques for treatment of epilepticseizures, to OSORIO et al; U.S. Pat. No. 5,299,569 entitled Treatment ofneuropsychiatric disorders by nerve stimulation, to WERNICKE et al; G.C. ALBERT, C. M. Cook, F. S. Prato, A. W. Thomas. Deep brainstimulation, vagal nerve stimulation and transcranial stimulation: Anoverview of stimulation parameters and neurotransmitter release.Neuroscience and Biobehavioral Reviews 33 (2009):1042-1060; GROVES D A,Brown V J. Vagal nerve stimulation: a review of its applications andpotential mechanisms that mediate its clinical effects. NeurosciBiobehav Rev 29(2005):493-500; Reese TERRY, Jr. Vagus nerve stimulation:a proven therapy for treatment of epilepsy strives to improve efficacyand expand applications. Conf Proc IEEE Eng Med Biol Soc. 2009;2009:4631-4634; Timothy B. MAPSTONE. Vagus nerve stimulation: currentconcepts. Neurosurg Focus 25 (3,2008):E9, pp. 1-4; ANDREWS, R. J.Neuromodulation. I. Techniques-deep brain stimulation, vagus nervestimulation, and transcranial magnetic stimulation. Ann. N. Y. Acad.Sci. 993(2003):1-13; LABINER, D. M., Ahern, G. L. Vagus nervestimulation therapy in depression and epilepsy: therapeutic parametersettings. Acta. Neurol. Scand. 115(2007):23-33; AMAR, A. P., Levy, M.L., Liu, C. Y., Apuzzo, M. L. J. Vagus nerve stimulation. Proceedings ofthe IEEE 96(7,2008):1142-1151; BEEKWILDER J P, Beems T. Overview of theclinical applications of vagus nerve stimulation. J Clin Neurophysiol27(2,2010):130-138; CLANCY J A, Deuchars S A, Deuchars J. The wonders ofthe Wanderer. Exp Physiol 98(1,2013):38-45].

Unlike conventional vagus nerve stimulation, which involves the surgicalimplantation of electrodes about the vagus nerve, in its preferredembodiment the present use of vagus nerve stimulation is non-invasive.Non-invasive procedures are distinguished from invasive procedures(including minimally invasive procedures) in that the invasiveprocedures insert a substance or device into or through the skin (orother surface of the body, such as a wound bed) or into an internal bodycavity beyond a body orifice. For example, transcutaneous electricalstimulation of a nerve is non-invasive because it involves attachingelectrodes to the skin, or otherwise stimulating at or beyond thesurface of the skin or using a form-fitting conductive garment, withoutbreaking the skin [Thierry KELLER and Andreas Kuhn. Electrodes fortranscutaneous (surface) electrical stimulation. Journal of AutomaticControl, University of Belgrade 18(2,2008):35-45; Mark R. PRAUSNITZ. Theeffects of electric current applied to skin: A review for transdermaldrug delivery. Advanced Drug Delivery Reviews 18 (1996) 395-425].

The present invention differs in several respects from previouslydisclosed applications of vagus nerve stimulation (VNS) to treatmigraine headaches. In particular, only invasive VNS had been reportedprior to Applicant's commonly assigned, co-pending patent applicationsconcerning the use of noninvasive VNS to treat migraine headache[application U.S. Ser. No. 13/109,250, Publication US20110230701,entitled Electrical and magnetic stimulators used to treatmigraine/sinus headache and comorbid disorders, to SIMON et al. andapplication U.S. Ser. No. 13/183,721, Publication US 20110276107,entitled Electrical and magnetic stimulators used to treatmigraine/sinus headache, rhinitis, sinusitis, rhinosinusitis, andcomorbid disorders, to SIMON et al. (which are hereby incorporated byreference)]. Furthermore, the parameters of stimulation that had beenused previously are different than the parameters that are disclosedhere [R M SADLER, R A Purdy & S Rahey. Vagal nerve stimulation abortsmigraine in patient with intractable epilepsy. Cephalalgia 22(2002),482-484; E. Daniela HORD, M. Steven Evans, Sajjad Mueed, BolaAdamolekun, and Dean K. Naritoku. The Effect of Vagus Nerve Stimulationon Migraines. The Journal of Pain 4 (9,2003): 530-534; Duncan A. GROVES,Verity J. Brown. Vagal nerve stimulation: a review of its applicationsand potential mechanisms that mediate its clinical effects. Neuroscienceand Biobehavioral Reviews 29 (2005) 493-500; A MAUSKOP. Vagus nervestimulation relieves chronic refractory migraine and cluster headaches.Cephalalgia 25(2005):82-86; M E LENAERTS, K J Oommen, J R Couch & VSkaggs. Can vagus nerve stimulation help migraine? Cephalalgia 28(2008),392-395; Alberto Proietti CECCHINI, Eliana Mea and Vincenzo Tullo,Marcella Curone, Angelo Franzini, Giovanni Broggi, Mario Savino, GennaroBussone, Massimo Leone. Vagus nerve stimulation in drug-resistant dailychronic migraine with depression: preliminary data. Neurol Sci 30 (Suppl1,2009):S101-S104; A. MAY and T. P. Jürgens. Therapeutic neuromodulationin primary headache syndromes (Therapeutische Neuromodulation beiprimären Kopfschmerzsyndromen). Nervenarzt 2010:doi_10.1007/s00115-010-3170-x; Patent application US20050216070,entitled Method and system for providing therapy for migraine/chronicheadache by providing electrical pulses to vagus nerve(s), to Boveja etal.].

The present invention also differs from earlier applications of VNS totreat migraine headache in that it relies on the measurement of evokedpotentials to select parameters for the electrical stimulation and totest whether a particular patient is a suitable candidate for treatmentusing VNS. Evoked potentials are physiological voltage differences,ordinarily measured on the patient's scalp, that are evoked by thepatient's experience of an event (event-related potentials). Thescalp-recorded evoked potentials arise from ionic currents within neuralnetworks of the patient's brain that are responses to the event. Mostcommonly (and in the present invention), the event that evokes thepotential is a brief sensory stimulus that is deliberately applied tothe patient. Examples of such stimuli are a flash of light, an audioclick, or an electrical shock that is applied to the patient's skin[William R. GOFF. Human average evoked potentials: procedures forstimulating and recording. Chapter 3, pp. 101-156 in: BioelectricRecording Techniques. Part B. Electroencephalography and Human BrainPotentials (Richard F. Thompson and Michale M. Patterson, eds). NewYork: Academic Press, 1974; David REGAN. Human Brain Electrophysiology.Evoked potentials and evoked magnetic fields in science and medicine.New York: Elsevier Science Publishing Co., 1989, pp. 1-672; Terence W.PICTON, Otavio G. Lins and Michael Scherg. The recording and analysis ofevent-related potentials. Chapter 1 (pp. 3-73) in Handbook ofNeuropsychology, Vol. 10 (F. Boller and J. Grafman, eds). Amsterdam:Elsevier Science B.V., 1995; Monica FABIANI, Gabriele Gratton andMichael G. H. Coles. Event Related Potentials. Methods, Theory, andApplications. Chapter 3, pp. 53-84 In: John T. Cacioppo, Louis G.Tassinary and Gary G. Berntson (eds). Handbook of Psychophysiology, 2ndEd. Cambridge: Cambridge University Press, 2000; Steven J. LUCK. Anintroduction to event-related potentials and their neural origins.Chapter 1 (pp. 1-50) in: Steven J. LUCK. An Introduction to theEvent-Related Potential Technique. Cambridge, Mass.: MIT Press, 2005;Todd C. HANDY (ed). Event-related Potentials: A Methods Handbook.Cambridge, Mass.: MIT Press, 2005, pp. 1-380; Steven J LUCK and Emily SKappenman, eds. Oxford handbook of event-related potential components.Oxford: Oxford University Press, 2012, pp. 1-626].

It was noted above that migraineurs exhibit sensory hyper-excitabilityduring the premonitory or prodromal phase of a migraine headache, aswell as during the headache phase itself. The hypersensitivity toexternal stimuli may manifest itself as photophobia, phonophobia,hyperosmia and cutaneous allodynia, corresponding respectively toheightened sensitivity to light, sound, odor, and touch (particularly ofthe scalp and face). For many years, evoked potential measurements havebeen performed on migraineurs in order to quantify abnormalities in theway in which they process sensory information. They may exhibit unusualevoked potential waveforms in response to a particular sensory stimulus,but the most striking aspect of the migraineur's processing of sensoryinformation is that their evoked potentials often do not habituate inthe same manner as normal individuals. Habituation is an adaptiveprocess in which evoked potentials decrease in amplitude when a sensorystimulus is presented to an individual over an extended period of time[MEGELA A L, Teyler T J. Habituation and the human evoked potential. JComp Physiol Psychol 93(6,1979):1154-1170]. Whereas normal individualsmay gradually reduce their response to repeated sensory stimuli, asevidenced by the magnitude of the corresponding evoked potential as afunction of time, the migraineur may maintain a constant (or evenincreased) responsiveness to the stimulus over a prolonged period oftime [AMBROSINI A, de Noordhout A M, Sändor P S, Schoenen J.Electrophysiological studies in migraine: a comprehensive review oftheir interest and limitations. Cephalalgia 23 (Suppl 1,2003):13-31; MVALERIANI, M de Tommaso, D Restuccia, D Le Pera, M Guido, G D lannetti,G Libro, A Truini, G Di Trapani, F Puca, P Tonali, G Cruccu. Reducedhabituation to experimental pain in migraine patients: a CO(2) laserevoked potential study. Pain 105(1-2,2003):57-64; AMBROSINI A, SchoenenJ. Electrophysiological response patterns of primary sensory cortices inmigraine. J Headache Pain 7(6,2006):377-388; COPPOLA G, Vandenheede M,Di Clemente L, Ambrosini A, Fumal A, De Pasqua V, Schoenen J.Somatosensory evoked high-frequency oscillations reflectingthalamo-cortical activity are decreased in migraine patients betweenattacks. Brain 128(Pt 1,2005):98-103; COPPOLA G, Pierelli F, Schoenen J.Habituation and migraine. Neurobiol Learn Mem 92(2,2009):249-259;COPPOLA G, lacovelli E, Bracaglia M, Serrao M, Di Lorenzo C, Pierelli F.Electrophysiological correlates of episodic migraine chronification:evidence for thalamic involvement. J Headache Pain 14(1,2013):76, pp.1-8; de TOMMASO M, Lo Sito L, Di Fruscolo O, Sardaro M, Pia PrudenzanoM, Lamberti P, Livrea P. Lack of habituation of nociceptive evokedresponses and pain sensitivity during migraine attack. Clin Neurophysiol116(6,2005):1254-1264; Neelam VANEY, Abhinav Dixit, Tandra Ghosh, RaviGupta, M. S. Bhatia. Habituation of event related potentials: a tool forassessment of cognition in headache patients. Delhi Psychiatry Journal11 (1, 2008):48-51].

Accordingly, it is one objective of the present invention to treatmigraineurs with non-invasive vagus nerve stimulation in such a way thattheir evoked potentials habituate, so as to more nearly resemble normalindividuals in that regard. Another objective of the invention is totest the migraineurs acutely with vagus nerve stimulation and thenpredict the likelihood that they will respond to noninvasive vagus nervestimulation over an extended period of time, in such a way that thefrequency and severity of chronic migraine attacks decreases. Attemptsto increase the habituation of evoked potentials to sensory stimuli havebeen made using drugs, but not with vagus nerve stimulation [DICLEMENTEL, Puledda F, Biasiotta A, Viganò A, Vicenzini E, Truini A, Cruccu G, DiPiero V. Topiramate modulates habituation in migraine: evidences fromnociceptive responses elicited by laser evoked potentials. J HeadachePain 14(1,2013):25, pp. 1-8]. Also, chronic invasive vagus nervestimulation has been described as affecting the location of some peaksand troughs in certain evoked potentials of epileptic patients, but ithas not been disclosed that noninvasive vagus nerve stimulation canaffect the habituation of evoked potentials, particularly in those ofmigraineurs [NARITOKU D K, Morales A, Pencek T L, Winkler D. Chronicvagus nerve stimulation increases the latency of the thalamocorticalsomatosensory evoked potential. Pacing Clin Electrophysiol 15(10 Pt2,1992):1572-1578].

The present invention may also be used to treat patients suffering fromfibromyalgia, which like migraine headache and other primary headaches,involves pain that is associated with abnormalities in the processing ofsensory signals. Unlike migraineurs, fibromyalgia sufferers experiencesignificant muscle pain, stiffness, and muscle fatigue as one of theirprimary complaints, which might be attributable to an over-sensitizationof nociceptors that are located in muscle or other deep tissues [ARNOLDL M. The pathophysiology, diagnosis and treatment of fibromyalgia.Psychiatr Clin North Am 33(2,2010):375-408; CLAUW D J, Arnold L M,McCarberg B H. The science of fibromyalgia. Mayo Clin Proc86(9,2011):907-911; CLAUW D J. Fibromyalgia: an overview. Am J Med122(12 Suppl,2009):S3-S13; Laurence A. BRADLEY. Pathophysiology ofFibromyalgia. Am J Med 122(12 Suppl,2009): S22; VIERCK, C. J. Amechanism-based approach to prevention of and therapy for fibromyalgia.Pain Research and Treatment, Article ID 951354 (2012), pp. 1-11].

In the United States, three medications are frequently used to treatfibromyalgia: pregabalin, duloxetine, and milnacipran, which actdifferently to influence transmission of sensory signals via centralnociceptive pathways [ARNOLD LM, Clauw D J, Dunegan L J, Turk D C; etal. A framework for fibromyalgia management for primary care providers.Mayo Clin Proc 87(5,2012):488-496; Jennifer FITZGIBBONS. The truth aboutfibromyalgia will help you help patients ease their pain. American NurseToday 2(9,2007):40-45]. However, there is a great deal of trial anderror in designing fibromyalgia treatment because of the heterogeneoussymptoms of the patients, so combination therapies are common. As analternative or complement to the use of medication, noninvasiveelectrical stimulation of the patient has also been used to treatfibromyalgia patients, involving the application of transcutaneouselectrical nerve stimulation to the patient's spine and leg [DAILEY D L,Rakel B A, Vance C G, Liebano R E, Amrit A S, Bush H M, Lee K S, Lee JE, Sluka K A. Transcutaneous electrical nerve stimulation reduces pain,fatigue and hyperalgesia while restoring central inhibition in primaryfibromyalgia. Pain 154(11,2013):2554-2562]. Cervical vagus nervestimulation has also been used to treat fibromyalgia, but this has onlyinvolved the use of invasive stimulation, not the noninvasivestimulation that is disclosed here. Furthermore, that work does notinvolve the measurement of evoked potentials [LANGE G, Janal M N,Maniker A, Fitzgibbons J, Fobler M, Cook D, Natelson B H. Safety andefficacy of vagus nerve stimulation in fibromyalgia: a phase I/II proofof concept trial. Pain Med 12(9,2011):1406-1413; U.S. Pat. No.8,457,748, entitled Vagus Nerve Stimulation for the Treatment ofFibromyalgia to Gudrun LANGE]. The occipital nerve has also beenstimulated electrically to treat fibromyalgia, but this too has notinvolved the use of evoked potentials [PLAZIER M, Dekelver I, VannesteS, Stassijns G, Menovsky T, Thimineur M, De Ridder D. Occipital NerveStimulation in Fibromyalgia: A Double-Blind Placebo-Controlled PilotStudy With a Six-Month Follow-Up. Neuromodulation. 2013 Oct. 7, pp.1-8]. U.S. Pat. No. 8,428,719, entitled Systems and Methods forRespiratory-Gated Auricular Vagal Afferent Nerve Stimulation, toNAPADOW, also discloses treatment of fibromyalgia (among other diseases)by a noninvasive method, but that disclosure only involves thestimulation of the auricular branch of the vagus nerve (not the cervicalvagus nerve), and it too does not involve the measurement of evokedpotentials.

It has been known for many years that some individuals have unusualvoluntary control over visceral functions, serving as apparentexceptions to the general rule that control of visceral organs isautonomous and non-voluntary. For example, some individuals are able tovoluntarily increase their heart rate at will [HF WEST and WE Savage.Voluntary acceleration of the heart beat. Archives of Internal Medicine22(1918):290-295; John T. KING, Jr. An instance of voluntaryacceleration of the pulse. Bull. Johns Hopkins Hosp. 31(1920): 303-305;H FEIL, H D Green, D Eiber. Voluntary acceleration of heart in a subjectshowing the Wolff-Parkinson-White syndrome: clinical, physiologic, andpharmacologic studies. Am Heart J. 34(3,1947):334-348].

It is conceivable that the rare individuals who can voluntarily controlautonomic functions such as heart rate, eye-pupil diameters,piloerection (“goose bumps” or cutis anserina), etc., do so via directneural connections between the portions of the brain involved involition and the central autonomic nervous system that connects toefferent visceral and motor nerves [LINDSLEY, D. B. and Sassaman, W. H.Autonomic activity and brain potentials associated with ‘voluntary’control of the pilomotors. Journal of Neurophysiology 1(1938):342-349].However, it is more plausible that the visceral control may be indirect,through voluntary muscular control that also affects the viscera, orthrough voluntary control over the circuits of the brain affectingemotions, which in turn affect the autonomic state of the viscera duringfear, anger, pain, joy, etc., or by otherwise taking advantage ofclassically acquired (Pavlovian) conditional reflexes [Joseph E. LEDOUX.Emotion circuits of the brain. Annu Rev Neurosci 23(2000):155-184;KREIBIG S D. Autonomic nervous system activity in emotion: a review.Biol Psychol 84 (3,2010):394-421; CRITCHLEY H D. Neural mechanisms ofautonomic, affective, and cognitive integration. J Comp Neurol493(1,2005):154-166; DWORKIN B R, Dworkin S. Learning of physiologicalresponses: II. Classical conditioning of the baroreflex. Behav Neurosci109(6,1995):1119-1136].

In the early 1960s, several publications suggested that most individualscould learn to voluntarily control autonomic functions, such as heartrate, vasoconstriction, salivation, intestinal contraction, and galvanicskin response, but they did not address the issue of direct versusindirect voluntary control [H. D. KIMMEL. Instrumental conditioning ofautonomically mediated behavior. Psychological Bulletin67(1967):337-345; H. D. KIMMEL. Instrumental conditioning ofautonomically mediated responses in human beings. American Psychologist29(5,1974):325-335]. A landmark publication in 1969 by MILLER had aprofound influence on work concerning whether the viscera could becontrolled directly and voluntarily [Neal E MILLER. Learning of visceraland glandular responses. Science 163(3866, 1969):434-445]. Thatpublication described the use of operant conditioning (also known asinstrumental conditioning or Skinnerian conditioning) to train animalsto control their heart rate and other visceral functions. Operantconditioning is distinguished from classical conditioning (Pavlovian orrespondent conditioning) in that operant conditioning deals with themodification of voluntary behavior, through the use of reinforcement andpunishment. Whereas Pavlovian responses are involuntarily reflexive andinvolve stimulus events that precede the learned response, in contrast,during operant conditioning, the reinforcement or punishment follows thelearned response that is performed voluntarily. In the experiments byMILLER and colleagues, animals were temporarily paralyzed with curareand were mechanically ventilated, in order to eliminate the possibilitythat muscular contraction was responsible for the purported learnedability to voluntarily change heart rate and other visceralphysiological variables that were investigated.

The results that were described by MILLER had broad implications andspawned a great deal of related work by other investigators over thefollowing two decades, particularly work that is described below as theuse of biofeedback [Neal E. MILLER. Biofeedback and visceral learning.Ann. Rev. Psychol. 29(1978):373-404]. However, his experimental resultswere eventually determined to be irreproducible and were retracted, andthe conduct of the assistant who performed much of the actual laboratorywork became suspect before he committed suicide [Barry R. DWORKIN andNeal E. Miller. Failure to replicate visceral learning in the acutecurarized rat preparation. Behavioral Neuroscience 100(3, 1986):299-314;Marion NOTT. Are the claims true? The Evening Independent (St.Petersburg, Fla.) Oct. 3, 1977, page 11]. Despite the still-frequentcitation of the work that MILLER has long since retracted, there iscurrently no credible evidence that any mammal can directly andvoluntarily control visceral autonomic functions, such as heart rate. Infact, it is thought that the direct, voluntary control of visceralautonomic functions is not possible in principle, unless it were to beaccompanied by the adaptation of internal bodily sensors that operatelargely below the level of consciousness (interoceptors, see below)[Barry R. DWORKIN. Learning and Physiological Regulation. Chicago:University of Chicago Press, 1993, Chapter 8, pp. 162-185]. However, asdescribed above, voluntary control over the viscera might be exertedindirectly via skeletal muscles or through voluntary modulation of anindividual's emotional state. With this in mind, one objective of thepresent invention is to teach methods and devices that actually enablemost individuals to directly and voluntarily control visceral autonomicfunctions, with or without simultaneous indirect voluntary control viaskeletal muscle or emotion.

One explanation for our inability to voluntarily control visceralfunction is that the conscious mind cannot generally sense the state ofthe viscera, so one would have little conscious basis for directingvoluntary visceral control, even if control over efferent nervesmodulating activity of the end organs could be voluntarily exercised. Infact, the body contains many types of internal sensors (interoceptors)that operate largely below the level of consciousness, includingbaroreceptors and mechanoceptors, chemoreceptors, thermoreceptors, andosmoreceptors. Sensors located in skeletal muscles, ligaments, andbursae (proprioceptors) sense information related to muscle strain,location and orientation. Sensors that respond to painful stimuli(nociceptors) may be like other interoceptors, except that theygenerally have a small diameter (A-delta and C fibers) and conveysignals to the central nervous system with a high frequency of dischargeonly after a threshold in the stimulus has been exceeded. In contrast toother peripheral sensors, nociceptors also do a poor job ofdiscriminating the location of the stimulus, and they convey theirsignals via a special anterolateral route up the spinal cord to thethalamus. To the extent that one is conscious of the state of theviscera, e.g., during painful internal stimuli (stomach ache, anginapectoris, etc.), that awareness appears to result from interoceptiverepresentation that first reaches the thalamus and eventually resides inthe brain's right anterior insula, working in conjunction with theadjoining frontal operculum and the anterior cingulate cortex [DieterVAITL. Interoception. Biological Psychology 42 (1996):1-27; CRITCHLEY HD, Wiens S, Rotshtein P, Ohman A, Dolan R J. Neural systems supportinginteroceptive awareness. Nat Neurosci 7(2,2004):189-195; CRAIG, A. D.How do you feel? Introception: the sense of the physiological conditionof the body. Nat. Rev. Neurosci 3(2002):655-666; CRAIG A D. How do youfeel—now? The anterior insula and human awareness. Nat Rev Neurosci10(1,2009):59-70].

In order to make an individual artificially conscious of the otherwiseunperceived state of an internal organ, investigators may electricallytransduce a physiological signal, then use the magnitude of that signalto generate a proportionate signal that may be sensed by one of theindividual's external senses. The generated signal is ordinarily anaudio or visual representation of the magnitude of the transducedphysiological signal. However, the generated signal may also be directedto another exteroceptive sense, e.g., using electrical stimulation,tactile stimulation with vibration or pressure, thermal stimulation, orolfactory stimulation. The individual whose physiological signal isbeing transduced may then voluntarily respond mentally to the magnitudeof the generated signal. To the extent that the individual learns tocontrol his or her body in such a way as to voluntarily modulate thevalue of the transduced physiological signal, then the patient is saidto have learned to perform biofeedback.

According to rules of the U.S. Food and Drug Administration, “abiofeedback device is an instrument that provides a visual or auditorysignal corresponding to the status of one or more of a patient'sphysiological parameters (e.g., brain alpha wave activity, muscleactivity, skin temperature, etc.) so that the patient can controlvoluntarily these physiological parameters . . . .” [21 CFR882.5050—Biofeedback device]. The individual will not necessarily beable to understand or explain how the voluntary control over thephysiological signal has been achieved. Such biofeedback may also beconsidered to be a form of instrumental operant learning, in which thereward to the individual is the satisfaction of being able tovoluntarily control the transduced physiological signal [Frank ANDRASIKand Amanda O. Lords. Biofeedback. Chapter 7, pp. 189-214 In: Lynda W.Freeman, ed. Mosby's Complementary & Alternative Medicine AResearch-based Approach. St. Louis, Mo.: Mosby Elsevier, 2009; John V.BASMAJIAN. Biofeedback—Principles and Practices for Clinicians, 3rd Edn.Baltimore: Williams & Wilkins, 1989 pp 1-396; Mark S. SCHWARTZ (ed).Biofeedback. A Practitioner's Guide (2nd. Ed). New York: Guilford Press,1995. pp 1-908].

Biofeedback methods and devices have been used in an attempt to managemany medical conditions, including migraine headache and fibromyalgia.Some such methods involve relaxation of muscles using electromyographic(EMG) biofeedback to counteract factors that contribute to the onset ofsymptoms. Other methods use biofeedback involving EEG or otherphysiological signals [William J. MULLALLY, Kathryn Hall M S, andRichard Goldstein. Efficacy of Biofeedback in the Treatment of Migraineand Tension Type Headaches. Pain Physician 12(2009):1005-1011; STOKES DA, Lappin M S. Neurofeedback and biofeedback with 37 migraineurs: aclinical outcome study. Behav Brain Funct 6(2010):9, pp. 1-10; YvonneNESTORIUC, Alexandra Martin, Winfried Rief, Frank Andrasik. BiofeedbackTreatment for Headache Disorders: A Comprehensive Efficacy Review. ApplPsychophysiol Biofeedback 33(2008):125-140; BABU A S, Mathew E, Danda D,Prakash H. Management of patients with fibromyalgia using biofeedback: arandomized control trial. Indian J Med Sci 61(8,2007):455-461; CARO X J,Winter E F. EEG biofeedback treatment improves certain attention andsomatic symptoms in fibromyalgia: a pilot study. Appl PsychophysiolBiofeedback 36(3,2011):193-200]. One objective of the present inventionis to treat headaches and fibromyalgia using improved biofeedbackmechanisms by making use of evoked potentials that are evoked by thestimulation of the vagus nerve.

SUMMARY

The present invention is concerned primarily with devices and methodsfor the treatment of medical disorders, such as migraine or otherprimary headaches, or of fibromyalgia, in which treatment involves thenoninvasive electrical stimulation of a cervical vagus nerve.

In one aspect of the invention, an evoked potential of the patient ismeasured and the signal delivered to the vagus nerve by the stimulatoris adjusted based upon the measured evoked potential in order tooptimize the signal and the treatment. Sensors used by the inventioninclude one or more electrodes applied to the scalp of the patient, inorder to measure the evoked potentials. However, the inventioncontemplates the use of many other types of physiological sensors aswell, particularly ones that are used for ambulatory monitoring.Parameters of the nerve stimulation impulse that can be varied includecertain aspects of the signal, such as the frequency, amplitude (voltageor current), duty cycle and/or the duration of the electrical impulse.Alternatively or additionally, the position and/or orientation of thestimulation device on the patient's neck may be adjusted based on theevoked potential. In certain embodiments, the device may be alternatedbetween the right and left side of the patient's neck to optimize thesignal based on the measurement of evoked potentials.

In another aspect of the invention, feedback provided by the system'ssensors is used to optimize the signal applied to the nerve. The use ofsuch feedback is useful in establishing an initial set of stimulationparameter values for an individual patient. Furthermore, the plotting ofsome feature(s) of the evoked potential waveform as a function of thevaried parameters of the electrical stimulation waveform may be used tocharacterize the electrophysiology of the individual patient(stimulus/response gain, threshold, saturation, linearity ornon-linearity, etc.). In fact, even the demonstrated ability to vary theevoked potential waveform as a function of the parameters of theelectrical stimulus waveform may be used to verify that the vagus nerveis in fact being stimulated, or that the position and/or orientation ofthe stimulation electrodes are optimal.

The system comprises software and hardware components allowing it to fixthe parameters of the electrical impulses once they have been optimized,based upon criteria that are sensed by the system's sensor(s).Thereafter, the system's signal generator is capable of applying thefixed electrical impulses to the patient. However, if the sensedproperties of the patient change over an extended period of time, thesystem may re-optimize the stimulation parameters as the need arises.

Once the stimulator is properly placed against the skin on the right orleft side of the neck of the patient, electrical impulses are appliedthrough the electrodes of the stimulator to the vagus nerve, to treatthe patient's condition or a symptom of that condition. For someconditions, the treatment may be acute, meaning that the electricalimpulse immediately begins to interact with one or more nerves toproduce a response in the patient. In some cases, the electrical impulsewill produce a response in the nerve(s) to improve the patient'scondition or symptom in less than 3 hours, preferably less than 1 hourand more preferably less than 15 minutes. For other conditions,intermittently scheduled or as-needed stimulation of the nerve mayproduce improvements in the patient over the course of several days,weeks, months or even years (i.e., chronic treatment). A more completedescription of such a device for the treatment of migraineurs can befound in one of applicant's co-pending patent applications referencedabove.

The noninvasive vagus nerve stimulator is configured to induce a peakpulse voltage sufficient to produce an electric field in the vicinity ofthe nerve, to cause the nerve to depolarize and reach a threshold foraction potential propagation. By way of example, the threshold electricfield for stimulation of the nerve may be about 8 V/m at 1000 Hz. Forexample, the device may produce an electric field within the patient ofabout 10 to 600 V/m (preferably less than 100 V/m) and/or an electricalfield gradient of greater than 2 V/m/mm. Electric fields that areproduced at the vagus nerve are generally sufficient to excite allmyelinated A and B fibers, but not necessarily the unmyelinated Cfibers. However, by using a suitable amplitude of stimulation,excitation of A-delta and B fibers may also be avoided.

In another aspect of the invention, devices and methods are disclosedfor modulating neurotransmitter levels within the central nervous systemof patients who have a demonstrable habituation deficit with regard totheir evoked potentials. In this embodiment, the patient may first betested by stimulating visual, auditory, or somatosensory sense organs(e.g., the cervical cutaneous senses) and measuring the correspondingevoked potentials, over an extended period of time. The patients who donot exhibit significant habituation in their evoked potentials, inresponse to the sensory stimulation over a prolonged period of time, arethen subjected to an acute stimulation of the vagus nerve. The patientis then retested by stimulating the sense organs and re-measuring thepreviously-measured evoked potentials. For some of the individuals (the“responders”), the effect of the intervening acute vagus nervestimulation is to significantly reduce the magnitude of features ofevoked potentials, thereby artificially effecting a form of evokedpotential habituation. Those individuals are therefore candidates forchronic treatment of their disorder (e.g., migraine headaches), byperforming the vagus nerve stimulation on a regular basis, with theobjective of reducing the duration, frequency and severity of symptomsassociated with the disorder.

The vagus nerve stimulation may also be useful for the treatment ofpatients irrespective of whether the patient exhibits a deficit in thehabituation of evoked potentials. When evoked potential measurements areperformed on populations of migraineurs and control normal individuals,before and after acute vagus nerve stimulation with differentstimulation parameters, statistical methods are used to determine whichfeatures of the pre- and post-stimulation evoked potentials, as well astheir differences, are most closely related to the acute reduction ofpain in the patient. Similar statistical methods are used to determinewhich features of the initial pre- and post-stimulation evokedpotentials, as well as their differences, are most closely related toreduction in the chronic frequency and severity of painful episodes.These data are then used to select patients as candidates for treatmentand to set nerve stimulation parameters.

In another aspect of the invention, one or more of the above-mentionedsensors may be used to perform biofeedback, in which output from thesensor is used to generate a biofeedback signal that can be experiencedby at least one of the patient's exteroceptive sense organs(time-varying audio signal, visual display, tactile signal, etc.). In anexemplary embodiment, the sensed property is a characteristic of anevoked potential, such as the amplitude of a peak or trough having aparticular latency, e.g., the amplitude of a P300 peak. The biofeedbacksignal is generally constructed to be proportional to the sensor'soutput. The patient then voluntarily uses conscious awareness of thatbiofeedback signal to mentally control a bodily function or structurethat modulates the amplitude of the neurophysiological property that ismeasured by the sensor, thereby completing the biofeedback loop.

In the present invention, one preferred method of providing abiofeedback signal to the patient is by electrically stimulating thecervical skin with a signal that varies according to the magnitude ofthe output of a physiological sensor. The electrodes that stimulate theskin are the same as the ones that may also be used to stimulate a vagusnerve that lies deeper under the electrodes and skin.

Treating the patients may also be implemented automatically(involuntarily) within the context of engineering control theory.Neurophysiological signals that are measured with sensors are presentedas input to a controller. The controller, comprising for example, thedisclosed nerve stimulator, a PID, and a feedback or feedforward model,then provides input to the patient via stimulation of a vagus nerve. Thevagus nerve stimulation in turn modulates components of the patient'snervous system, such as the autonomic nervous system, which results inmodulation of the physiological properties that are measured withsensors, thereby completing the automatic control loop. The modulatedcomponents of the patient's nervous system may include particularresting state networks, such as the default mode network.

In another aspect of the invention, interoceptive representation that ispresented to—and is represented in—the brain's right anterior insula andrelated structures, may be derived in part from artificial or virtualsignals that correspond to stimulation of fibers in the vagus nerve,rather from the ordinary signaling of bodily interoceptors. The patientmay be conscious of the artificial interoception and may use it tomentally control a bodily function or structure that modulates theamplitude of the physiological property that is measured by thephysiological sensor. Thus, the invention contemplates a voluntary,conscious response to the artificial interoception, even though itoriginates from vagus nerve stimulation rather than from stimulation ofan exteroceptive sense as in biofeedback.

In the most general configuration of the disclosed devices and methods,the three above-mentioned mechanisms (biofeedback, direct stimulation ofthe vagus nerve to effect automatic control, and artificialinteroceptive sensation) will collectively modulate the targetneurophysiological system, interacting with one another to determine thevalue of the sensed physiological signal. Part of the interaction isdetermined by the manner in which the nerve stimulator/biofeedbackdevice/neurophysiological controller is programmed. For example, directstimulation of the neurophysiological system via the vagus nerve may beprogrammed to follow and amplify or enhance changes in the measuredsensor values that occur as a result of biofeedback. In otherembodiments, both biofeedback and vagus nerve stimulation are performedsimultaneously, and mathematical modeling is used to infer thephysiological effects that are due to the biofeedback, thereby allowingthe device to infer the conscious intentions of the patient and applythe vagus nerve stimulation accordingly. For the subset of individualswho are unable to control their neurophysiological signals adequatelyusing biofeedback, even after multiple training attempts, and even withamplification of biofeedback effects using vagus nerve stimulation asindicated above, the device may also be programmed to use vagus nervestimulation alone to automatically perform the neurophysiologicalcontrol.

In a preferred embodiment of the invention, an electrical stimulatorhousing comprises a source of electrical power and two or more remoteelectrodes that are configured to stimulate the vagus nerve. Thestimulator may comprise two electrodes that lie side-by-side, whereinthe electrodes are separated by electrically insulating material. Eachelectrode is in continuous contact with an electrically conductingmedium that extends from the patient-interface element of the stimulatorto the electrode. The interface element contacts the patient's skin whenthe device is in operation.

The system may also comprise a docking station that is used to charge arechargeable battery within the stimulator housing. The docking stationand stimulator housing may also transmit data to one another. They mayalso transmit data to, and receive data from, a computer program in apatient interface device, such as a mobile phone or nearby computer.Physiological sensors may transmit their signals to the stimulator,docking station, and/or interface device. Such data transmission ispreferably wireless, but wired communication between devices is alsocontemplated.

For stimulation of a deep nerve, current passing through electrodes ofthe stimulator may be about 0 to 40 mA, with voltage across theelectrodes of about 0 to 30 volts. The current is passed through theelectrodes in bursts of pulses. There may be 1 to 20 pulses per burst,preferably five pulses. Each pulse within a burst has a duration ofabout 20 to 1000 microseconds, preferably 200 microseconds. A burstfollowed by a silent inter-burst interval repeats at 1 to 5000 burstsper second (bps, similar to Hz), preferably at 15-50 bps, and even morepreferably at 25 bps. The preferred shape of each pulse is a fullsinusoidal wave.

The preferred stimulator shapes an elongated electric field of effectthat can be oriented parallel to a long nerve, such as a vagus. Byselecting a suitable waveform to stimulate the nerve, along withsuitable parameters such as current, voltage, pulse width, pulses perburst, inter-burst interval, etc., the stimulator produces acorrespondingly selective physiological response in an individualpatient. Such a suitable waveform and parameters are simultaneouslyselected to avoid substantially stimulating nerves and tissue other thanthe target nerve, avoiding the stimulation of nerves in the skin thatproduce pain, but optionally stimulating receptors in the skin that maybe used for biofeedback purposes.

In a minimally invasive embodiment of the invention, a stimulationdevice comprises one or more electrodes and a pulse generator and isconfigured for implantation at a target site adjacent to or near thecervical vagus nerve. The energy that is used to produce the impulses isreceived wirelessly by a dipole or other type of antenna that is alsopart of the stimulator. The received energy is preferably from far-fieldor approximately plane wave electromagnetic waves in the frequency rangeof about 0.3 to 10 GHz, more preferably about 800 MHz to 6 GHz and evenmore preferably about 800 MHz to 1.2 GHz. In an exemplary embodiment,the carrier signal is around 915 MHz. The electrical energy istransmitted from the antenna of an external energy source that ispreferably a meter or more outside the patient, but that may also besituated closer or even be placed within the patient. In someembodiments, the transmitter may be worn around the neck as a pendant,placed in a pocket, attached to a belt or watch, or clipped to clothing.

The novel systems, devices and methods for treating medical conditionsare more completely described in the following detailed description ofthe invention, with reference to the drawings provided herewith, and inclaims appended hereto. Other aspects, features, advantages, etc. willbecome apparent to one skilled in the art when the description of theinvention herein is taken in conjunction with the accompanying drawings.

INCORPORATION BY REFERENCE

Hereby, all issued patents, published patent applications, andnon-patent publications that are mentioned in this specification areherein incorporated by reference in their entirety for all purposes, tothe same extent as if each individual issued patent, published patentapplication, or non-patent publication were specifically andindividually indicated to be incorporated by reference.

This application refers to the following patents and patentapplications, the entire disclosures of which are hereby incorporated byreference for all purposes: U.S. patent application Ser. No. 13/279,437filed Oct. 24, 2011, U.S. patent application Ser. No. 13/222,087 filedAug. 31, 2011, U.S. patent application Ser. No. 13/183,765 filed Jul.15, 2011, U.S. patent application Ser. No. 13/183,721 filed Jul. 15,2011, U.S. patent application Ser. No. 13/109,250 filed May 17, 2011,U.S. patent application Ser. No. 13/075,746 filed Mar. 30, 2011, U.S.patent application Ser. No. 13/005,005 filed Jan. 12, 2011, U.S. patentapplication Ser. No. 12/964,050 filed Dec. 9, 2010, U.S. patentapplication Ser. No. 12/859,568 filed Aug. 9, 2010, U.S. patentapplication Ser. No. 12/408,131 filed Mar. 20, 2009, U.S. patentapplication Ser. No. 12/612,177 filed Nov. 9, 2009 now U.S. Pat. No.8,041,428 issued Oct. 18, 2011, U.S. patent application Ser. No.12/859,568, filed Aug. 19, 2010, U.S. patent application Ser. No.13/208,425, filed Aug. 12, 2011, U.S. patent application Ser. No.12/964,050, filed Dec. 9, 2010, U.S. patent application Ser. No.13/005,005, filed Jan. 12, 2011, U.S. application Ser. No. 13/024,727,filed Feb. 10, 2011, U.S. application Ser. No. 13/075,746, filed Mar.30, 2011, U.S. application Ser. No. 13/109,250, filed May 17, 2011, U.S.application Ser. No. 13/183,721, filed Jul. 15, 2011, US applicationSer. No. 13/222,087, filed Aug. 31, 2011, U.S. application Ser. No.13/357,010, filed Jan. 24, 2012, U.S. application Ser. No. 13/736,096,filed Jan. 8, 2013, U.S. application Ser. No. 13/603,781, filed Sep. 5,2012, U.S. application Ser. No. 13/671,859, filed Nov. 8, 2012, U.S.application Ser. No. 13/731,035, filed Dec. 30, 2012, U.S. applicationSer. No. 13/858,114, filed Apr. 8, 2013, and U.S. application Ser. No.14/071,577, filed Nov. 4, 2013.

BRIEF DESCRIPTION OF DRAWINGS

For the purposes of illustrating the various aspects of the invention,there are shown in the drawings forms that are presently preferred, itbeing understood, however, that the invention is not limited by or tothe precise data, methodologies, arrangements and instrumentalitiesshown, but rather only by the claims.

FIGS. 1A-1B provide schematic diagrams for the operation of: (FIG. 1A) aconventional evoked potential measurement device and (FIG. 1B) a closedloop nerve stimulator, evoked potential measurement device and/orbiofeedback, according to the present invention.

FIG. 2 shows a schematic view of nerve modulating devices according tothe present invention, which supply controlled pulses of electricalcurrent to body-surface electrodes.

FIGS. 3A-3C illustrate front (FIG. 3A) and back (FIG. 3B) views of adual-electrode stimulator according to an embodiment of the presentinvention, which is shown to attach to a docking station (FIG. 3C).

FIGS. 4A-4B show an assembled (FIG. 4A) and expanded (FIG. 4B) view ofone of the stimulator heads that were shown in FIGS. 3A-3C.

FIGS. 5A-5D show some types of devices that may communicate with thedocking station and/or stimulator shown in FIG. 3, comprising a remotecontrol (FIG. 5A), a mobile phone (FIG. 5B), a touchscreen device (FIG.5C), and a laptop computer (FIG. 5D).

FIG. 6 shows an expanded diagram of the control unit shown in FIG. 2,separating components of the control unit into those within the body ofthe stimulator, those within the docking station, and those withinhand-held and internet-based devices, also showing communication pathsbetween such components.

FIG. 7 illustrates the approximate position of the housing of thestimulator according one embodiment of the present invention, when usedto stimulate the right vagus nerve in the neck of an adult patient.

FIG. 8 illustrates the approximate position of the housing of thestimulator according one embodiment of the present invention, when usedto stimulate the right vagus nerve in the neck of a child.

FIGS. 9A-9C illustrate the vertebrae and major vessels of the neck,including vessels within the carotid sheath (FIG. 9A), as well asmuscles that lie in the vicinity of those vessels, namely, the platysmamuscle (FIG. 9B) and sternocleidomastoid muscle (FIG. 9C).

FIG. 10 illustrates the housing of the stimulator according oneembodiment of the present invention, when positioned to stimulate avagus nerve in the patient's neck, wherein the stimulator is applied tothe surface of the neck in the vicinity of the identified anatomicalstructures.

FIGS. 11A-11C show exemplary electrical voltage/current profiles andwaveforms for stimulating and/or modulating impulses that are applied toa nerve, including a representation of the relation between stimulationpulses and physiological activity (FIG. 11A), and the shape of the anexemplary applied waveform on a short (FIG. 11B) and longer (FIG. 11C)time scale.

FIG. 12 shows structures within a patient's nervous system that may bemodulated by electrical stimulation of a vagus nerve.

FIG. 13 shows functional networks within the brain (resting statenetworks) that may be modulated by electrical stimulation of a vagusnerve.

FIGS. 14A-14B show an evoked potential resulting from noninvasivestimulation of a patient's vagus nerve (FIG. 14A), and the correspondingevoked potential when the stimulator is repositioned slightly so as toavoid stimulation of the vagus nerve (FIG. 14B).

FIGS. 15A-15C illustrate an embodiment of the nerve stimulator,including a schematic view of a nerve modulating system (implantablelead module or electrical stimulator) according to one or more aspectsof the present invention (FIG. 15A); a schematic view of an implantablestimulation device according to the present invention (FIG. 15B); and amore specific view (FIG. 15C) of the components of one embodiment of theimplantable stimulation device shown in FIG. 15B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the present invention, electrodes applied to the skin of the patientgenerate electrical current or voltage impulses within tissue of thepatient. One of the objectives of the invention is to apply theelectrical impulses so as to interact with intrinsic signals of one ormore nerves, in order to achieve a therapeutic result, with or withoutthe simultaneous provision of a biofeedback signal to the patient. Muchof the disclosure will be directed specifically to treatment of apatient by electrical stimulation in or around a vagus nerve, withdevices positioned non-invasively on or near a patient's neck. Asrecognized by those having skill in the art, the methods should becarefully evaluated prior to use in patients known to have preexistingcardiac issues. It will also be appreciated that the devices and methodsof the present invention can be applied to other tissues and nerves ofthe body, including but not limited to other parasympathetic nerves,sympathetic nerves, spinal or cranial nerves.

Prior art is shown in FIG. 1A, which illustrates components involved ina conventional evoked potential (EP) measurement. The investigatorinitiates the generation of one or more sensory stimuli from astimulator generator, such as a flash of light, an audio click, orbipolar transcutaneous electrical stimulation applied on the skin overthe median, ulnar, peroneal, or posterior tibial nerve [William R. GOFF.Human average evoked potentials: procedures for stimulating andrecording. Chapter 3, pp. 101-156 in: Bioelectric Recording Techniques.Part B. Electroencephalography and Human Brain Potentials (Richard F.Thompson and Michale M. Patterson, eds). New York: Academic Press, 1974;David REGAN. Human Brain Electrophysiology. Evoked potentials and evokedmagnetic fields in science and medicine. New York: Elsevier SciencePublishing Co., 1989, pp. 1-672; Terence W. PICTON, Otavio G. Lins andMichael Scherg. The recording and analysis of event-related potentials.Chapter 1 (pp. 3-73) in Handbook of Neuropsychology, Vol. 10 (F. Bollerand J. Grafman, eds). Amsterdam: Elsevier Science B.V., 1995; MonicaFABIANI, Gabriele Gratton and Michael G. H. Coles. Event RelatedPotentials. Methods, Theory, and Applications. Chapter 3, pp. 53-84 In:John T. Cacioppo, Louis G. Tassinary and Gary G. Berntson (eds).Handbook of Psychophysiology, 2nd Ed. Cambridge: Cambridge UniversityPress, 2000; Steven J. LUCK. An introduction to event-related potentialsand their neural origins. Chapter 1 (pp. 1-50) in: Steven J. LUCK. AnIntroduction to the Event-Related Potential Technique. Cambridge, Mass.:MIT Press, 2005; Todd C. HANDY (ed). Event-related Potentials: A MethodsHandbook. Camridge, Mass.: MIT Press, 2005, pp. 1-380; Steven J LUCK andEmily S Kappenman, eds. Oxford handbook of event-related potentialcomponents. Oxford: Oxford University Press, 2012, pp. 1-626]. Apain-associated evoked potential may also be initiated using a laserlight pulse that is applied to the skin of the subject [TREEDE R D,Lorenz J, Baumgärtner U. Clinical usefulness of laser-evoked potentials.Neurophysiol Clin 33(6,2003):303-314; GARCIA-LARREA L, Frot M, ValerianiM. Brain generators of laser-evoked potentials: from dipoles tofunctional significance; Neurophysiol Clin 33(6,2003):279-292]. Thestimulus then activates visual, auditory, somatosensory, or painexteroceptive sense organ receptors, respectively, in the subject of themeasurement. The neural responses of the sensory receptors are thentransmitted to structures within the central nervous system, whichinitially process the sensory information without consciousparticipation of the subject. However, those structures are also incommunication with structures in the central nervous system that make itpossible for the subject to subsequently become conscious of the sensoryinformation, for example, by recognizing the novelty or significance ofthe stimulus.

As also shown in FIG. 1A, electrode sensors placed at well-definedlocations on the scalp of the subject make it possible to measureelectrical potentials that are evoked as the underlying structures ofthe central nervous system processes the sensory information, bothunconsciously and consciously. Such neural processing generates ioniccurrent flows within a brain of the subject that can be measured on thescalp. Actual measurement of the potentials is triggered by the activityof the sensory stimulus generator, so that the measured potentials aretime-locked relative to the onset of the stimulus. When a transientresponse EP is measured, the EP waveform ordinarily consists of a seriesof peaks and valleys relative to the baseline potential, which arecharacterized by their amplitudes (positive or negative), as well astheir times of occurrence relative to the stimulus (their latencies).The potentials that are so-measured are a mixture of the neural activityof structures involved in both the unconscious and conscious processingof the sensory information, as may be inferred by performing the EPmeasurement when the subject is or is not anesthetized, or awake versusasleep. Transient response EP data acquisition equipment may also becapable of averaging multiple successive evoked potentials (so as toincrease the signal-to-noise of the EP data) and also automaticallylocate peaks or other features in the evoked potential waveform, such asa P300 peak that corresponds to a conscious evaluation on the part ofthe patient that the stimulus is interesting [KNIGHT R T, Scabini D.Anatomic bases of event-related potentials and their relationship tonovelty detection in humans. J Clin Neurophysiol 15(1,1998):3-13; KECECIH, Degirmenci Y, Atakay S. Habituation and dishabituation of P300. CognBehav Neurol 19(3,2006):130-134].

Peaks and troughs in the transient response EP may often be identifiedby comparing their properties with those found in normative databases.Artifacts that appear in the EP may also be identified and preferablyeliminated. In the case of electrical stimulation this may include ashock or stimulus artifact that is due to conduction through the skinfrom the stimulus to the recording electrode. It may also be a myogenicartifact that originates in scalp muscles in the vicinity of recordingelectrodes, or other muscles, and may be identified, for example, by theuse of chemical muscle relaxants that cause the artifact to disappear.

The transient EP is produced as a response to a single brief stimulus,and for purposes of signal-averaging, the response is not evoked againuntil the potential has returned to its value prior to the stimulus. Incontrast, a steady state EP is produced in response to stimuli that arerepeated periodically, even though the potential may not have had timeto return to its baseline value between stimuli. Such a steady-state EPwill also exhibit a reproducible waveform, but because the waveform isdependent on factors such as the frequency of stimulus repetition, it isconventionally characterized in terms of its Fourier spectrum. However,it may also be characterized in terms of the amplitude and latency ofpeaks and troughs corresponding to the temporal summation of synapticpotentials [David REGAN. Distinction between the transient andsteady-state responses of a system. Section 1.3, pp. 34-43 in: DavidREGAN. Human Brain Electrophysiology. Evoked potentials and evokedmagnetic fields in science and medicine. New York: Elsevier SciencePublishing Co., 1989; ZAKHAROVA I, Kornhuber M E. Facilitation of latesomatosensory evoked potentials by electrical train stimuli. NeurosciLett 557(Pt B,2013):135-137].

Embodiments of the present invention are shown in FIG. 1B, which aredifferent from the prior art shown in FIG. 1A in several respects.First, in its non-invasive embodiment, it involves transcutaneouselectrical stimulation applied to the skin over the vagus nerve in theneck, rather than the median, posterior tibial, or other nerves that aretypically used in somatosensory evoked potential work. The vagus nerveat that cervical location comprises on the order of 100,000 axons thatserve a large number of autonomic, sensory, and motor functions that arequantitatively and qualitatively greater than those served by themedian, tibial, or other such nerves. Similarly, the vagus nerve axonsat that cervical location serve many more functions than branches of thevagus nerve at other locations, such as auricular branch at the tragusof the ear. Therefore, the range of physiological effects that may beproduced by the device shown in FIG. 1B is correspondingly greater thanthose that may be produced by the stimulation of other nerves or othervagal nerve branches.

As indicated in FIG. 1B the investigator initiates the operation of avagus nerve stimulator, which generates cervical electrical stimulationthrough electrodes placed on the surface of the neck of the subject. Thestimulation may involve the application of one or more superimposedstimulation waveforms, the parameters of which determine whether thestimulation preferably affects only receptors in the patient's skin,and/or whether the stimulation reaches the underlying vagus nerve. Thesomatosensory electrical stimulus used in FIG. 1A to stimulate nerves isordinarily a monophasic square wave pulse having a duration of 100microsecond to 1 second. In contrast, the devices shown in FIG. 1B useelectrical stimulation waveforms that may be biphasic, bursting,sinusoidal and otherwise differ from monophasic square waves, inaddition to the possibility that they involve the superposition ofwaveforms that are directed to the vagus nerve and cutaneous receptors.The stimulus waveforms produced by the devices shown in FIG. 1B may beeither single-shot (to generate transient EP responses) or periodic (togenerate steady-state EP responses).

FIG. 1B illustrates a closed-loop (feedback or biofeedback) system foracquiring evoked potential data. Unlike the system shown in FIG. 1A, thevagus nerve stimulator device may control and vary successive sensorystimuli, once the investigator has initiated its operation. Thus, inFIG. 1B, the vagus nerve stimulator may trigger the generation of thecervical sensory stimulus on its own, based upon its analysis ofprevious transient or steady-state evoked potentials that it hadreceived from the scalp electrodes and/or from the analysis of otherphysiological data that it has received from other physiologicalsensors. Examples of such other physiological data are electrodermalvoltages measured from sites such as the subject's hand or respiratorydata that have been measured using impedance pneumography sensors.

The evoked potentials that are processed by such feedback methods may insome situations be generated primarily by the central nervous systemstructures for unconscious sensory processing. As an example of suchfeedback methods, the vagus nerve stimulator may vary a parameter of thestimulus waveform (e.g. amplitude, or frequency in the case ofsteady-state EP measurement), measure the resulting EP waveform, againvary the parameter based on that waveform measurement, and then repeatthis procedure iteratively until it results in an EP waveform thatexhibits preferred features that lie within some specified range. Theuse of such feedback would be particularly useful in establishing aninitial set of stimulation parameter values for an individual,considering that different individuals may vary significantly withrespect to the details of their preferred electrical stimulationwaveforms. Furthermore, the plotting of some feature(s) of the EPwaveform as a function of the varied parameters of the electricalstimulation waveform may be used to characterize the electrophysiologyof the individual patient (stimulus/response gain, threshold,saturation, linearity or non-linearity, etc.). In fact, even thedemonstrated ability to vary the EP waveform as a function of theparameters of the electrical stimulus waveform may be used to verifythat the vagus nerve is in fact being stimulated, or that the positionand/or orientation of the stimulation electrodes are optimal.

In other situations, the relevant features of the evoked potentials maybe generated primarily by the central nervous system structures that areinvolved in conscious neural processing and control. As an example ofthat situation, the individual may consciously react to the sensationsthat result from the vagus nerve stimulation, as evidenced by theappearance of a P300 peak in his/her transient evoked potential. Afterdetecting the P300 peak, the device can use that fact to vary theparameters of the next vagus nerve stimulation. For example, the P300peak may appear once the stimulation amplitude reaches a sensorythreshold that is recognized by the subject, or the properties of theP300 peak may change when the stimulation amplitude is so large that itproduces pain. Because in that embodiment of the invention theindividual is consciously controlling the operation of the device viathe P300 peak, this evoked potential application is a type ofbiofeedback, rather than purely automatic feedback.

Note that the type of biofeedback that is described above is differentfrom other types of biofeedback, known as neurofeedback, that alsomeasure potentials with scalp electrodes. This is because neurofeedbackmeasures spontaneous (EEG) potentials, rather than evoked potentials.Thus, in neurofeedback, subjects are typically presented with an audiotone whenever their EEG contains significant EEG waves of a particulartype (e.g., alpha, beta, high beta, theta, or sensorimotor). Someindividuals can concentrate on the tone and then learn to voluntarilysuppress and/or enhance the time spent in that EEG state, as evidencedby their ability to voluntarily increase or decrease the amplitude ofthe tone [John N. DEMOS. Getting Started with Neurofeedback. New York:W.W. Norton & Co., 2005. pp. 1-281].

Another novel feature of the system shown in FIG. 1B is that it may beused to train an individual to consciously and voluntarily control the“other physiological system” that is labeled in the figure. In such abiofeedback application, the skin at the subject's neck is stimulated inproportion to a previous or concurrently measured property of the “otherphysiological system” (e.g., electrodermal voltage measured on thesubject's hand), such that the subject is made consciously aware of themagnitude of the measured physiological property through the magnitudeof the skin stimulation. Alternatively, the stimulation applied to thesubject's neck is a function of the features of the measured evokedpotential (e.g., amplitude or latency of one or more particular EPwaveform peaks or troughs). The subject then attempts to mentallycontrol the magnitude of the skin stimulation, and thereby consciouslycontrol the magnitude of the measured physiological property throughthought alone. The electrical signals that simulate cutaneous nerveswithin the skin may be analog signals that vary in some continuous wayrelative to the physiological property that is being transduced.Alternatively, the biofeedback signals may be digital, comprisingrecognizable coded pulse trains, as has been suggested in connectionwith tactile communication devices for the blind. For example,electrocutaneous signals with three discrete intensity levels and threediscrete long-pulse durations can be discriminated [R. H. GIBSON.Electrical stimulation of pain and touch. pp. 223-261. In: D. R.Kenshalo, ed. The Skin Senses. Springfield, Ill.: Charles C Thomas,1968; Erich A. PFEIFFER. Electrical stimulation of sensory nerves withskin electrodes for research, diagnosis, communication and behavioralconditioning: A survey. Medical and Biological Engineering.6(6,1968):637-651; Alejandro HERNANDEZ-ARIETA, Hiroshi Yokoi, TakashiOhnishi, Tamio Arai. An f-MRI study of an EMG Prosthetic HandBiofeedback System. In: T. Arai et al. (Eds.). IAS-9, Proceedings of the9th International Conference on Intelligent Autonomous Systems,University of Tokyo, Tokyo, Japan, Mar. 7-9, 2006, Amsterdam: IOS Press,2006, pp. 921-929; Kahori KITA, Kotaro Takeda, Rieko Osu, SachikoSakata, Yohei Otaka, Junichi Ushiba. A Sensory feedback system utilizingcutaneous electrical stimulation for stroke patients with sensory loss.Proc. 2011 IEEE International Conference on Rehabilitation Robotics,Zurich, Switzerland, Jun. 29-Jul. 1, 2011, 2011:5975489, pp 1-6].

It is understood that although the biofeedback component of FIG. 1B maybe configured to use only electrical stimulation of the skin, the systemmay be configured to use additional sensory modalities as well, such asaudio or visual biofeedback signals. However, for the present invention,the use of audio and visual sensory stimuli would ordinarily be usedinstead to evoke auditory or visual evoked potentials. Thus, FIG. 1Bcontains components “Other sensory stimuli” and “Other Sense Organs”that may refer to the stimulation of auditory or visual senses. In thatsituation, the vagus nerve stimulator/biofeedback device may alsoproduce stimuli that stimulate vision or hearing (e.g., a flash of lightor a click), thereby producing visual or auditory evoked potentials.Those “other sense organ” evoked potentials may then be measured via thescalp electrodes, and selected quantitative properties of the evokedpotentials may then be automatically extracted by the vagus nervestimulator/biofeedback device. Those properties may then be presented asa cutaneous sensation to the subject, via cervical electricalstimulation. In this embodiment, the subject becomes aware of themagnitude of the “other sense organ” evoked potential through themagnitude of the cutaneous sensation as biofeedback. It is understoodthat the cutaneous sensation itself may contribute to the evokedpotential waveform, and preliminary experiments are used to distinguishwhich features of the EP waveform are due to the cutaneous stimulationand which are due to the “other sense organ”, such that the EP waveformfeature used for the biofeedback arises primarily from stimulation ofthe “other sense organ.”

The subject may then endeavor, using thought alone, to consciouslyincrease or decrease the magnitude of the measured evoked potentialproperty that is produced by stimulation of the “other sense organ”, asthe magnitude of the property is supplied as a cutaneous biofeedbacksignal. The learned ability to control that property would beparticularly valuable to individuals who suffer from migraine headaches,because they often suffer from what is known as a deficit ofhabituation. Whereas the evoked potentials from normal individualsgenerally decrease in magnitude as the corresponding stimulus is appliedover an extended period of time (habituation), the evoked potentialsfrom migraineurs often do not. Thus, if the migraineur is able to learnto consciously reduce the magnitude of features of the evoked potential(effectively, to habituate the EP), his or her EP electrophysiology willbecome more nearly like that of a normal individual, so that thelikelihood of the subject's migraine headaches may thereby be reduced.[MEGELA A L, Teyler T J. Habituation and the human evoked potential. JComp Physiol Psychol. 93(6,1979):1154-1170; AMBROSINI A, de Noordhout AM, Sándor P S, Schoenen J. Electrophysiological studies in migraine: acomprehensive review of their interest and limitations. Cephalalgia 23(Suppl 1,2003):13-31; AMBROSINI A, Schoenen J. Electrophysiologicalresponse patterns of primary sensory cortices in migraine. J HeadachePain 7(6,2006):377-388; COPPOLA G, Vandenheede M, Di Clemente L,Ambrosini A, Fumal A, De Pasqua V, Schoenen J. Somatosensory evokedhigh-frequency oscillations reflecting thalamo-cortical activity aredecreased in migraine patients between attacks. Brain128(Pt1,2005):98-103; COPPOLA G, Pierelli F, Schoenen J. Habituation andmigraine. Neurobiol Learn Mem 92(2,2009):249-259; COPPOLA G, lacovelliE, Bracaglia M, Serrao M, Di Lorenzo C, Pierelli F. Electrophysiologicalcorrelates of episodic migraine chronification: evidence for thalamicinvolvement. J Headache Pain 14(1,2013):76, pp. 1-8; de TOMMASO M, LoSito L, Di Fruscolo O, Sardaro M, Pia Prudenzano M, Lamberti P, LivreaP. Lack of habituation of nociceptive evoked responses and painsensitivity during migraine attack. Clin Neurophysiol116(6,2005):1254-1264; VALERIANI M, de Tommaso M, Restuccia D, Le PeraD, Guido M, lannetti G D, Libro G, Truini A, Di Trapani G, Puca F,Tonali P, Cruccu G. Pain 105(1-2,2003):57-64. Reduced habituation toexperimental pain in migraine patients: a CO(2) laser evoked potentialstudy; Neelam VANEY, Abhinav Dixit, Tandra Ghosh, Ravi Gupta, M. S.Bhatia. Habituation of event related potentials: a tool for assessmentof cognition in headache patients. Delhi Psychiatry Journal1(1,2008):48-51].

Generally, the devices shown in FIG. 1B will also be used to directlystimulate the vagus nerve, in addition to, or instead of, stimulatingsensory nerves within the skin. As described below and in co-pending,commonly assigned patent application U.S. Ser. No. 13/222,087, entitledDevices and methods for non-invasive capacitive electrical stimulationand their use for vagus nerve stimulation on the neck of a patient, toSIMON et al. (which is hereby incorporated by reference), Applicant hasdeveloped a stimulator device that can noninvasively stimulate a vagusnerve directly in the patient's neck, without producing cutaneousdiscomfort to a patient. When the vagus nerve is being stimulated by thedevice, the quality of sensation in the patient's skin above the vagusnerve depends strongly on the stimulation current and frequency, suchthat when the currents are not much greater than the perceptionthreshold, the cutaneous sensations may be described as tingle, itch,vibration, buzz, touch, pressure, or pinch. For situations in which theskin is being stimulated with a constant current and with a particulartype of stimulation waveform that is described below, any such cutaneoussensation may be ignored by the patient, and the stimulator does notserve as an exteroceptive biofeedback device. In that case, the deviceresembles instead a physiological control device that may be used tostimulate structures of the central nervous system and/or “Otherphysiological systems”, via stimulation of the vagus nerve, as indicatedin FIG. 1B. The particular structures of the central nervous system orother physiological systems that are affected by the vagus nervestimulation depend on the parameters of the vagus nerve stimulation,which are selected to stimulate the particular system. Direct electricalstimulation of the vagus nerve will itself generate evoked potentials,as the resulting vagal action potentials and their sequelae propagatewithin the central nervous system.

In certain aspects of the invention, the measurement of an evokedpotential as described above may be used to optimize non-invasivestimulation of the vagus nerve with, for example, one of the devicesdescribed below. Given that a particular evoked potential can bequantified that represents stimulation of the vagus nerve, the operatorcan use this measurement to confirm that the action potentials have beencreated in the vagus nerve during electrical stimulation. In thismanner, the operator may, for example, vary a characteristic of theelectrical impulses generator by the vagus nerve stimulator in order toensure that such stimulation is effectively stimulating the vagus nerveat a therapeutic level. For example, if such stimulation does notinitially generate the evoked potentials that would confirm the firingof the action potentials in the vagus nerve, the operator may varyaspects of the signal, such as the amplitude, frequency, pulse widthand/or duty cycle until such an evoked potential is generated. Inaddition or alternatively, the operator may vary the placement ororientation of the device on the subject's neck to ensure properstimulation of the vagus nerve. As another alternative, the operator mayposition the vagal nerve stimulator on the other side of the patient'sneck (left to right or vice versa) in an attempt to optimize thestimulation.

One application of direct vagus nerve stimulation at the neck is tomodulate neurotransmitter levels within the central nervous system ofpatients with certain medical disorders such as primary headache (e.g.,migraine), or fibromyalgia, who have a demonstrable habituation deficitwith regard to their evoked potentials. Thus, the patient may be tested(without feedback or biofeedback) by stimulating “other sense organs” orthe cervical cutaneous senses in FIG. 1B, and measuring thecorresponding evoked potentials, over an extended period of time (e.g.,visual, auditory, or traditional somatosensory EPs, as reviewed inCOPPOLA G, Pierelli F, Schoenen J. Habituation and migraine. NeurobiolLearn Mem 92(2,2009):249-259). The patients who do not exhibitsignificant habituation in their evoked potentials, in response to thesensory stimulation over a prolonged period of time, are then subjectedto an acute direct stimulation of the vagus nerve. The patient is thenretested (again without feedback or biofeedback) by stimulating “othersense organs” and re-measuring the previously-measured evoked potentials(visual, auditory, or traditional somatosensory EPs). For some of theindividuals (the “responders”), the effect of the intervening acutevagus nerve stimulation is to significantly reduce the magnitude offeatures of evoked potentials, thereby artificially effecting a form ofEP habituation. Those individuals are therefore candidates for chronictreatment of their migraine headaches, by performing the vagus nervestimulation on a regular basis, with the objective of reducing theduration, frequency and severity of symptoms associated with thedisorder (e.g., migraine attacks, pain associated with fibromyalgia,etc). Methods for doing so were disclosed in the co-pending, commonlyassigned patent application U.S. Ser. No. 13/109,250, entitledElectrical and magnetic stimulators used to treat migraine/sinusheadache and comorbid disorders, to SIMON et al, and U.S. Ser. No.13/183,721 entitled Electrical and magnetic stimulators used to treatmigraine/sinus headache, rhinitis, sinusitis, rhinosinusitis, andcomorbid disorders, to SIMON et al. On the other hand, some individuals(the “non-responders”) may exhibit no significant changes to themagnitude of features of their evoked potentials following acutestimulation of their vagus nerve. It may be decided on the basis of thisoutcome that the “non-responders” are candidates for treatment bymethods other than performing vagus nerve stimulation on a regular basis[OZKUL Y, Bozlar S. Effects of fluoxetine on habituation of patternreversal visually evoked potentials in migraine prophylaxis. Headache42(7,2002):582-587].

Vagus nerve stimulation may also be useful for the treatment of patientsirrespective of whether the patient exhibits a deficit in thehabituation of evoked potentials, and irrespective of whether the vagusnerve stimulation promotes the normalization of habituation of evokedpotentials. In migraineurs, for example, the likely usefulness of thevagus nerve stimulation may more generally be based primarily upon thebaseline characteristics of an evoked potential, measured during one ormore phases of the migraine headache, particularly during the interictalphase. In fact, it is preferable to perform the measurements duringmultiple times throughout the interictal phase, in view of the changesin the evoked potential that occur throughout that phase. A method forusing previously measured values of characteristics of the baselineevoked potential, to infer the likelihood of therapeutic success, is asfollows. If the migraine attack is in progress, noninvasive vagus nervestimulation is administered, and its effect on the reduction of headachepain is measured. The pain measurement may be based on self-reporting ofthe patient, or it may be based on an objective physiologicalmeasurement of pain. The measurement of pain may also be made followingstimulation with multiple sets of vagus nerve stimulation parameters, inorder to evaluate the stimulation parameters that have the greatesteffect on the reduction of pain. After vagus nerve stimulation, theevoked potential may be measured again, and the features of the baselineevoked potential may then be compared with features of thepost-stimulation evoked potential. Changes in the evoked potential mayinvolve differences in amplitudes and latencies of peaks and troughs,which are of potential predictive value. When such measurements areperformed on populations of migraineurs and control normal individuals,statistical methods may then be used to determine which features of thepre- and post-stimulation evoked potentials, as well as theirdifferences, are most closely related to the reduction of pain in themigraineur. The statistical methods may also be used to predict whichparameters of the vagus nerve stimulation have the greatest effect onthe reduction of pain and on the features of the pre- andpost-stimulation evoked potentials. The vagus nerve stimulation may thenbe re-applied to the patient, with a different set of stimulationparameters, selected on the basis of the relation between thoseparameters and pain reduction, as well as on characteristics of the pre-and/or post-stimulation evoked potentials.

The vagus nerve stimulation may also be used as a prophylaxis to reducethe frequency or severity of migraine attacks. In that case, the vagusnerve stimulation is applied to the patient over a prolonged period oftime, and its quantitative effects on the frequency and severity of themigraine attacks is measured. When such measurements are performed onpopulations of migraineurs and control normal individuals, statisticalmethods may then be used to determine which features of the initial pre-and post-stimulation evoked potentials, as well as their differences,are most closely related to reduction in the chronic frequency andseverity of migraine attacks. Thereafter, the likelihood that vagusnerve stimulation will be successful in treating a migraineurchronically may be inferred from the measured features of his/herinitial pre- and post-stimulation evoked potentials, as well asdifferences between the pre- and post-stimulation evoked potentials.

Although the electrical stimulation embodiment described in the previousparagraph does not make use of a cutaneous biofeedback signal, in otherembodiments, the patient may nevertheless become conscious of directstimulation of the vagus nerve, as an artificial interoceptivesensation. Interoceptive sensations from the body's interoceptors areconveyed to, and represented in, the brain's right anterior insula andrelated structures, at which locations the individual may be consciousof interoceptive activity. As described below, some of the neuralpathways leading to the insula involve afferent fibers of the vagusnerve. Interoceptors within the body may convey naturally-occurringinteroceptive signals via vagal afferent fibers, but in the presentinvention, electrical stimulation of the vagus nerve may also produceartificial interoceptive signals. Thus, the present inventioncontemplates the stimulation of vagal afferent fibers in such a way thatthe patient may sense the stimulation as an internal bodily signal, eventhough the signals are not produced by interoceptors. When theartificial interoceptive signals are varied by the nerve stimulator as afunction of the output of a physiological sensor or some feature of anevoked potential waveform, the individual may consciously respond to theartificial interoceptive signals as though they were a biofeedbacksignal. This is despite the fact that the signals are not conventionalbiofeedback signals, because they are not presented to an exteroceptivesense.

In a commonly-assigned, co-pending application, (Ser. No. 14/071,577,entitled Nerve Stimulator System, filed Nov. 4, 2013) Applicantsdisclosed the implantation and use of minimally invasive cervical vagusnerve stimulators. For such stimulators, the cutaneous (e.g. tactile)stimulation shown in FIG. 1B is not feasible unless additionalskin-surface electrodes were to be applied to the subject. Nevertheless,in such applications, the individual may also consciously respond to theartificial interoceptive signals that are applied through the minimallyinvasive vagus nerve stimulator, as though they were a biofeedbacksignal. Otherwise, the biofeedback methods that are disclosed hereinwould have to be performed using sensory modalities that do not involvecervical electrical stimulation, for example, by using auditory orvisual biofeedback that is produced through the “Other Sensory Stimuli”component of FIG. 1B.

In a more general embodiment of the system shown in FIG. 1B, a cutaneousbiofeedback signal may be superimposed upon the electrical stimulationwaveform that preferentially stimulates the vagus nerve directly. Thus,in addition to the mechanisms described in the previous two paragraphs,the stimulation waveform may also contain a time-varying signal withfrequency components that are designed specifically to stimulatecutaneous nerves. The biofeedback signal will vary as a function of thephysiological parameter that is being sensed by the physiological sensor(e.g., evoked potential feature or skin conductance level). Thebiofeedback signal may be a continuous analog signal, or it may be adigital signal, e.g., with three discrete intensity levels and threediscrete long-pulse durations that can be discriminated. The patient maythen consciously respond to the biofeedback signal, for example, byrelaxing or tensing skeletal muscles or by eliciting a relaxing oragitated emotional response, thereby modulating the tone of thesympathetic nervous system [COSTA F, Biaggioni I. Role of adenosine inthe sympathetic activation produced by isometric exercise in humans. JClin Invest. 93(1994):1654-1660; KREIBIG S D. Autonomic nervous systemactivity in emotion: a review. Biol Psychol 84 (3,2010):394-421].

The three mechanisms illustrated in FIG. 1B (biofeedback, artificialinteroceptive sensation, and direct stimulation via the vagus nerve)will collectively modulate the central nervous system or otherphysiological systems, interacting with one another to determine thevalue of the sensed physiological signal or feature of the evokedpotential. Part of the interaction is determined by the manner in whichthe vagus nerve stimulator/biofeedback device/feedback controller isprogrammed. For example, direct stimulation of the physiological systemvia the vagus nerve may be programmed to follow and amplify or enhancechanges that occur as a result of biofeedback. An embodiment of thatexample would occur when the individual uses galvanic skin responsebiofeedback alone to consciously reduce sympathetic tone throughmuscular and emotional modulation, whereupon the device in FIG. 1Bsenses that reduction through its programming and then amplifies theeffect by increasing parasympathetic tone after a brief time delay, bydirectly stimulating vagal parasympathetic efferent nerve fibers.

In this example, it is clear what the biofeedback effect is initially(reduction of sympathetic tone), and the vagus stimulation is onlyapplied thereafter to amplify it (stimulation of vagal parasympatheticfibers). In other embodiments that are disclosed herein, bothbiofeedback and vagus nerve stimulation are performed simultaneously,and mathematical modeling is used to infer the effects that are due tothe biofeedback, thereby allowing the device to also infer theintentions of the individual and apply the vagus nerve stimulationaccordingly. Consequently, the whole device shown in FIG. 1B has morefunctionality than its individual parts simply added together.

In certain embodiments, the system comprises software and hardwarecomponents to fix the parameters of the electrical impulses after theyhave been optimized. In one aspect, feedback provided by thephysiological sensor optimizes the signal applied to the nerve. Once thesignal has been optimized, the software and hardware components of thesystem fix the electrical impulse based on the parameters that have beensensed by the physiological sensor. The signal generator will then applythe fixed electrical impulse to the patient. For example, the physicianmay be able to optimize the electrical impulse in the hospital or officesetting by applying electrical impulses and measuring their effect oncertain body parameters. The impulses can then be varied either manuallyor automatically until the effect is optimized. If the stimulator isimplanted, the signal generator may automatically apply the optimizedelectrical impulse to the patient at certain times throughout the day,or it may be designed to only apply the electrical impulses whenactivated by the patient. If the stimulator is a non-invasive device,the patient self-treats and applies the optimized electrical impulsesaccording to the treatment algorithm set up by the physician.

There is little prior art involving both vagus nerve stimulation andbiofeedback devices, where the term “biofeedback device” means hereessentially what is defined in 21 CFR 882.5050: “a biofeedback device isan instrument that provides a visual or auditory signal [or other suchexteroceptive signal] corresponding to the status of one or more of apatient's physiological parameters (e.g., brain alpha wave activity,muscle activity, skin temperature, etc.) so that the patient can controlvoluntarily these physiological parameters . . . .” The term biofeedbackappears in the text of some patents or patent applications, but oftenwith a different meaning than what is meant here. Examples of suchdifferent usages of the term are as follows. U.S. Pat. No. 7,657,310,entitled Treatment of reproductive endocrine disorders by vagus nervestimulation, to BURAS, uses the term biofeedback to refer to feedback ofa signal that has been transduced from a patient's body, but notvoluntary mental control over such a signal. U.S. Pat. No. 8,509,902,entitled Medical device to provide breathing therapy, to CHO et al.,discloses devices and methods that are said to involve biofeedback, butin fact, their invention is not concerned with voluntary control over abiofeedback signal because it “relates generally to the use of diaphragmcontraction prolongation during breathing therapy sessions (e.g., when apatient is not cognitive of respiratory control, such as when they aresleeping) . . . ” U.S. Pat. No. 7,946,976, entitled Methods and devicesfor the surgical creation of satiety and biofeedback pathways, toGERTNER, uses the term biofeedback to mean an internal bodily controlsignal, not the voluntary control over a biofeedback signal derived froma physiological measurement. Patent application US20050149142, entitledGastric stimulation responsive to sensing feedback, to STARKEBAUM, usesthe term biofeedback to mean artificially-produced symptoms ofgastroparesis that are caused by electrical stimulation of the stomach.

However, some patents or patent applications do use the term biofeedbackin the sense that is intended here and also mention vagus nervestimulation. Application US 20120071731, entitled System and method forphysiological monitoring, to GOTTESMAN, describes the use of aphysiological sensor that can be used in a biofeedback application andthat can also be used to determine when to stimulate a vagus nerve.However, the biofeedback and vagus nerve stimulation uses of the sensorare described as being different applications. Similarly, U.S. Pat. No.8,036,736, entitled Implantable systems and methods for identifying acontraictal condition in a subject, to SNYDER et al., is concerned withthe analysis of physiological signals for purposes of automaticidentification of circumstances under when an epilepsy patient shouldundertake therapy. SNYDER mentions vagus nerve stimulation andbiofeedback techniques as two such alternative therapies, but not asmethods that should be performed together.

Patent application US 20100004705, entitled Systems, Methods and devicesfor treating tinnitus, to KILGARD et al. and US 20100003656, entitledSystems, methods and devices for paired plasticity, to KILGARD et al,also apparently use the term biofeedback in the sense that is intendedhere. They describe the simultaneous use of electrical neuralstimulation with biofeedback therapy (among other therapies), includingthe use of invasive vagus nerve stimulation. However, according toKILGARD et al., the disclosed relation between the biofeedback therapyand neural stimulation relates only to their mutual timing. There isnothing in their application to suggest that the actual parameters ofthe nerve stimulation are to be modulated in conjunction with thestrength of the biofeedback signal itself or of the physiological signalthat serves as the basis of the biofeedback signal. Furthermore, in thatpatent application, the electrical stimulation and biofeedback signalsare described as being distinct entities, wherein the electricalstimulation is shown in the figures there to be an invasive procedure,and biofeedback is generally understood to be a noninvasive procedure.This is in contrast to the present invention, in which the electricalstimulation itself may comprise the biofeedback signal, and in whichboth the electrical nerve stimulation and biofeedback methods arenoninvasive procedures. Also, according to KILGARD et al, the electricalstimulation is said to induce plasticity in the brain, e.g., viaactivation of the nucleus basalis, locus coeruleus, or amygdala, therebyenhancing efficacy of the biofeedback therapy. However, the presentinvention does not necessarily involve neuronal plasticity, and thepresent invention may also produce stimulation of the nucleus basalis,locus coeruleus, amygdala, and many other brain components, withoutinducing plasticity. Furthermore, the present invention is differentfrom all of the above-mentioned patents concerning biofeedback involvingthe vagus nerve in that the present biofeedback methods and devicesinvolve the measurement of evoked potentials.

Description of the Noninvasive Nerve Stimulating/Modulating Devices

Devices of the present invention are able to stimulate a vagus nerve, aswell as the skin above the nerve, as now described. An embodiment of thepresent invention is shown in FIG. 2, which is a schematic diagram of anelectrode-based nerve stimulating/modulating device 302 for deliveringimpulses of energy to nerves for the treatment of medical conditions. Asshown, device 302 may include an impulse generator 310; a power source320 coupled to the impulse generator 310; a control unit 330 incommunication with the impulse generator 310 and coupled to the powersource 320; and electrodes 340 coupled via wires 345 to the impulsegenerator 310. In a preferred embodiment, the same impulse generator310, power source 320, and control unit 330 may be used for either amagnetic stimulator or the electrode-based stimulator 302, allowing theuser to change parameter settings depending on whether magnetic coils orthe electrodes 340 are attached, either of which may be used for thetherapeutic stimulation applications that are describe herein[application Ser. No. 13/183,765 and Publication US2011/0276112,entitled Devices and methods for non-invasive capacitive electricalstimulation and their use for vagus nerve stimulation on the neck of apatient, to SIMON et al.; application Ser. No. 12/964,050 andPublication US2011/0125203, entitled Magnetic Stimulation Devices andMethods of Therapy, to SIMON et al, which are hereby incorporated byreference].

Although a pair of electrodes 340 is shown in FIG. 2, in practice theelectrodes may also comprise three or more distinct electrode elements,each of which is connected in series or in parallel to the impulsegenerator 310. Thus, the electrodes 340 that are shown in FIG. 2represent all electrodes of the device collectively.

The item labeled in FIG. 2 as 350 is a volume, contiguous with anelectrode 340, that is filled with electrically conducting medium. Theconducting medium in which the electrode 340 is embedded need notcompletely surround an electrode. The volume 350 is electricallyconnected to the patient at a target skin surface in order to shape thecurrent density passed through an electrode 340 that is needed toaccomplish stimulation of the patient's nerve or tissue such as theskin. The electrical connection to the patient's skin surface is throughan interface 351. In one embodiment, the interface is made of anelectrically insulating (dielectric) material, such as a thin sheet ofMylar. In that case, electrical coupling of the stimulator to thepatient is capacitive. In other embodiments, the interface compriseselectrically conducting material, such as the electrically conductingmedium 350 itself, or an electrically conducting or permeable membrane.In that case, electrical coupling of the stimulator to the patient isohmic. As shown, the interface may be deformable such that it isform-fitting when applied to the surface of the body. Thus, thesinuousness or curvature shown at the outer surface of the interface 351corresponds also to sinuousness or curvature on the surface of the body,against which the interface 351 is applied, so as to make the interfaceand body surface contiguous. The control unit 330 controls the impulsegenerator 310 to generate a signal for each of the device's electrodes(or magnetic coils). The signals are selected to be suitable foramelioration of a particular medical condition, when the signals areapplied non-invasively to a target nerve or tissue via the electrodes340. It is noted that nerve stimulating/modulating device 302 may bereferred to by its function as a pulse generator. Patent applicationpublications US2005/0075701 and US2005/0075702, both to SHAFER, containdescriptions of pulse generators that may be applicable to the presentinvention. By way of example, a pulse generator is also commerciallyavailable, such as Agilent 33522A Function/Arbitrary Waveform Generator,Agilent Technologies, Inc., 5301 Stevens Creek Blvd Santa Clara Calif.95051.

The control unit 330 may also comprise a general purpose computer,comprising one or more CPU, computer memories for the storage ofexecutable computer programs (including the system's operating system)and the storage and retrieval of data, disk storage devices,communication devices (such as serial and USB ports) for acceptingexternal signals from the system's keyboard, computer mouse, andtouchscreen, as well as any externally supplied physiological signals(see FIG. 1B), analog-to-digital converters for digitizing externallysupplied analog signals such as evoked potentials and physiologicalsignals (see FIG. 1B), communication devices for the transmission andreceipt of data to and from external devices such as printers and modemsthat comprise part of the system, hardware for generating the display ofinformation on monitors that comprise part of the system, and busses tointerconnect the above-mentioned components. Thus, the user may operatethe system by typing instructions for the control unit 330 at a devicesuch as a keyboard and view the results on a device such as the system'scomputer monitor, or direct the results to a printer, modem, and/orstorage disk. Control of the system may be based upon feedback,including biofeedback, measured from externally supplied physiologicalor environmental signals (see FIG. 1B). Alternatively, the control unit330 may have a compact and simple structure, for example, wherein theuser may operate the system using only an on/off switch and powercontrol wheel or knob. In a section below, a preferred embodiment isdescribed wherein the stimulator housing has a simple structure, butother components of the control unit 330 are distributed into otherdiscrete devices (see FIG. 6).

Parameters for the nerve or tissue stimulation include power level,frequency and train duration (or pulse number). The stimulationcharacteristics of each pulse, such as depth of penetration, strengthand selectivity, depend on the rise time and peak electrical energytransferred to the electrodes, as well as the spatial distribution ofthe electric field that is produced by the electrodes. The rise time andpeak energy are governed by the electrical characteristics of thestimulator and electrodes, as well as by the anatomy of the region ofcurrent flow within the patient. In one embodiment of the invention,pulse parameters are set in such as way as to account for the detailedanatomy surrounding the nerve that is being stimulated [Bartosz SAWICKI,Robert Szmurlo, Przemyslaw Plonecki, Jacek Starzyński, StanislawWincenciak, Andrzej Rysz. Mathematical Modelling of Vagus NerveStimulation. pp. 92-97 in: Krawczyk, A. Electromagnetic Field, Healthand Environment: Proceedings of EHE'07. Amsterdam, IOS Press, 2008].Pulses may be monophasic, biphasic or polyphasic. Embodiments of theinvention include those that are fixed frequency, where each pulse in atrain has the same inter-stimulus interval, and those that havemodulated frequency, where the intervals between each pulse in a traincan be varied. The preferred pulse parameters are described in a latersection of this application.

Preferred Embodiments of the Electrode-Based Stimulator

The electrodes of the invention are applied to the surface of the neck,or to some other surface of the body, and are used to deliver electricalenergy non-invasively to a nerve. The vagus nerve has previously beenstimulated non-invasively, using electrodes applied via leads to thesurface of the skin. It has also been stimulated non-electricallythrough the use of mechanical vibration [HUSTON J M, Gallowitsch-PuertaM, Ochani M, Ochani K, Yuan R, Rosas-Ballina M et al (2007).Transcutaneous vagus nerve stimulation reduces serum highmobility groupbox 1 levels and improves survival in murine sepsis. Crit Care Med 35:2762-2768; GEORGE M S, Aston-Jones G. Noninvasive techniques for probingneurocircuitry and treating illness: vagus nerve stimulation (VNS),transcranial magnetic stimulation (TMS) and transcranial direct currentstimulation (tDCS). Neuropsychopharmacology 35(1,2010):301-316].However, no such reported uses of noninvasive vagus nerve stimulationwere directed to biofeedback applications. Patent No. U.S. Pat. No.7,340,299, entitled Methods of indirectly stimulating the vagus nerve toachieve controlled asystole, to John D. PUSKAS, discloses thestimulation of the vagus nerve using electrodes placed on the neck ofthe patient, but that patent is unrelated to biofeedback. Non-invasiveelectrical stimulation of the vagus nerve has also been described inJapanese patent application JP2009233024A with a filing date of Mar. 26,2008, entitled Vagus Nerve Stimulation System, to Fukui YOSHIHOTO, inwhich a body surface electrode is applied to the neck to stimulate thevagus nerve electrically. However, that application is also unrelated tobiofeedback. In patent publication US20080208266, entitled System andmethod for treating nausea and vomiting by vagus nerve stimulation, toLESSER et al., electrodes are used to stimulate the vagus nerve in theneck to reduce nausea and vomiting, but this too is unrelated tobiofeedback.

Patent application US2010/0057154, entitled Device and method for thetransdermal stimulation of a nerve of the human body, to DIETRICH etal., discloses a non-invasive transcutaneous/transdermal method forstimulating the vagus nerve, at an anatomical location where the vagusnerve has paths in the skin of the external auditory canal. Theirnon-invasive method involves performing electrical stimulation at thatlocation, using surface stimulators that are similar to those used forperipheral nerve and muscle stimulation for treatment of pain(transdermal electrical nerve stimulation), muscle training (electricalmuscle stimulation) and electroacupuncture of defined meridian points.The method used in that application is similar to the ones used in U.S.Pat. No. 4,319,584, entitled Electrical pulse acupressure system, toMcCALL, for electroacupuncture; U.S. Pat. No. 5,514,175 entitledAuricular electrical stimulator, to KIM et al., for the treatment ofpain; and U.S. Pat. No. 4,966,164, entitled Combined sound generatingdevice and electrical acupuncture device and method for using the same,to COLSEN et al., for combined continuous and monotonoussound/electroacupuncture. A related application is US2006/0122675,entitled Stimulator for auricular branch of vagus nerve, to LIBBUS etal. Similarly, U.S. Pat. No. 7,386,347, entitled Electric stimulator foralpha-wave derivation, to CHUNG et al., described electrical stimulationof the vagus nerve at the ear. Patent application US2008/0288016,entitled Systems and Methods for Stimulating Neural Targets, to AMURTHURet al., also discloses electrical stimulation of the vagus nerve at theear. U.S. Pat. No. 4,865,048, entitled Method and apparatus for drugfree neurostimulation, to ECKERSON, teaches electrical stimulation of abranch of the vagus nerve behind the ear on the mastoid processes, inorder to treat symptoms of drug withdrawal. KRAUS et al describedsimilar methods of stimulation at the ear [KRAUS T, Hosl K, Kiess O,Schanze A, Kornhuber J, Forster C (2007). BOLD fMRI deactivation oflimbic and temporal brain structures and mood enhancing effect bytranscutaneous vagus nerve stimulation. J Neural Transm 114: 1485-1493].However, none of the disclosures in these patents or patent applicationsfor electrical stimulation of the vagus nerve near the ear are used toin connection with biofeedback.

Embodiments of the present invention may differ with regard to thenumber of electrodes that are used, the distance between electrodes, andwhether disk or ring electrodes are used. In preferred embodiments ofthe method, one selects the electrode configuration for individualpatients, in such a way as to optimally focus electric fields andcurrents onto the selected nerve, without generating excessive currentson the surface of the skin. This tradeoff between focality and surfacecurrents is described by DATTA et al. [Abhishek DATTA, Maged Elwassif,Fortunato Battaglia and Marom Bikson. Transcranial current stimulationfocality using disc and ring electrode configurations: FEM analysis. J.Neural Eng. 5 (2008): 163-174]. Although DATTA et al. are addressing theselection of electrode configuration specifically for transcranialcurrent stimulation, the principles that they describe are applicable toperipheral nerves as well [RATTAY F. Analysis of models forextracellular fiber stimulation. IEEE Trans. Biomed. Eng. 36 (1989):676-682].

A preferred embodiment of an electrode-based stimulator is shown in FIG.3. As shown, the stimulator (30) comprises two heads (31) and aconnecting part that joins them. Each head (31) contains a stimulatingelectrode. The connecting part of the stimulator contains the electroniccomponents and a battery (not shown) that are used to generate thesignals that drive the electrodes. However, in other embodiments of theinvention, the electronic components that generate the signals that areapplied to the electrodes may be separate, but connected to theelectrode head (31) using wires or wireless communication with theheads. Furthermore, other embodiments of the invention may contain asingle such head or more than two heads.

Heads of the stimulator (31) are applied to a surface of the patient'sbody, during which time the stimulator may be held in place by straps orframes or collars, or the stimulator may be held against the patient'sbody by hand. In either case, the level of stimulation power may beadjusted with a wheel (34) that also serves as an on/off switch. A light(35) is illuminated when power is being supplied to the stimulator. Anoptional cap may be provided to cover each of the stimulator heads (31),to protect the device when not in use, to avoid accidental stimulation,and to prevent material within the head from leaking or drying. Thus, inthis embodiment of the invention, mechanical and electronic componentsof the stimulator (impulse generator, control unit, and power source)are compact, portable, and simple to operate.

Details of preferred embodiments of the stimulator heads are describedin co-pending, commonly assigned applications that were cited in thesection Cross Reference to Related Applications. As described in thoseapplications, the stimulator designs situate the electrodes of thestimulator (340 in FIG. 2) remotely from the surface of the skin, withina chamber that is filled with conducting material (350 in FIG. 2). Thus,the conducting material is placed in a chamber between the electrode andthe exterior component of the stimulator head that contacts the skin(351 in FIG. 2), thereby allowing for current to pass from the electrodeto the skin. An embodiment of a stimulator head 31 is shown in FIG. 4.FIG. 4A shows a section through one of the two stimulator heads 31 thatare shown in FIG. 3. The outer structure of the stimulator head 31supports the chamber 32 that is filled with conducting material 350. Theelectrode 340 is shown in FIG. 4A to be a conducting metal screw, towhich a wire (345 in FIG. 2) from the stimulator's impulse generator(310 in FIG. 2) is attached. The interface 351 of the stimulator head,which contacts the surface of the skin, is shown in FIG. 4A to comprisea disc that is made of a conducting metal, such as stainless steel.Assembly of the interface 351, chamber 32, and electrode 340 isillustrated in FIG. 4B with an exploded view. The conducting material350 may be added to the chamber 32 before the electrode 340 is screwedinto the chamber 32.

One of the novelties of such a design is that the stimulator, along witha correspondingly suitable stimulation waveform (see below), shapes theelectric field, producing a selective physiological response bystimulating that nerve, but avoiding substantial stimulation of nervesand tissue other than the target nerve, particularly avoiding thestimulation of nerves that produce pain. The design may, however,stimulate tactile nerves of the skin by superimposing stimulationwaveforms that are directed individually to the deep nerve and to theskin nerves. The shaping of the electric field is described in terms ofthe corresponding electromagnetic field equations in co-pending,commonly assigned application US20110230938 (application Ser. No.13/075,746), entitled Devices and methods for non-invasive electricalstimulation and their use for vagal nerve stimulation on the neck of apatient, to SIMON et al., which is hereby incorporated by reference.

Significant portions of the control unit (330 in FIG. 2) of the vagusnerve stimulator may reside in controller components that are physicallyseparate from the housing of the stimulator (30 in FIG. 3). In suchembodiments, separate components of the controller and stimulatorhousing may generally communicate with one another wirelessly. Thus, theuse of wireless technology avoids the inconvenience, size constraints,and distance limitations of interconnecting cables. A more completerationale for physically separating components of the control unit isprovided in a commonly assigned, co-pending application entitled MEDICALSELF-TREATMENT USING NON-INVASIVE VAGUS NERVE STIMULATION, to SIMON etal., which is hereby incorporated by reference.

Accordingly, an embodiment of the invention includes a docking station(40 in FIG. 3C) that may also be used as a recharging power supply forthe stimulator housing (30 in FIG. 3). The docking station maysend/receive data to/from the stimulator housing, and may send/receivedata to/from databases and other components of the system, includingthose that are accessible via the internet. Thus, prior to anyparticular stimulation session, the docking station may load into thestimulator parameters of the session, including stimulation waveformparameters.

In a preferred embodiment, the docking station also limits the amount ofstimulation energy that may be consumed by the patient in thestimulation session, by charging the stimulator's rechargable batterywith only a specified amount of releasable electrical energy. Note thatthis is generally different than setting a parameter to restrict theduration of a stimulation session. As a practical matter, the stimulatormay therefore use two batteries, one for stimulating the patient (thecharge of which may be limited by the docking station) and the other forperforming other functions such as data transmission. Methods forevaluating a battery's charge or releasable energy are known in the art,for example, in U.S. Pat. No. 7,751,891, entitled Power supplymonitoring for an implantable device, to ARMSTRONG et al. Alternatively,control components within the stimulator housing may monitor the amountof stimulation energy that has been consumed during a stimulationsession and stop the stimulation session when a limit has been reached,irrespective of the time when the limit has been reached.

Refer now to the docking station that is shown as item 40 in FIG. 3C.The stimulator housing 30 and docking station 40 can be connected to oneanother by inserting the connector 36 near the center of the base 38 ofthe stimulator housing 30 into a mated connector 42 of the dockingstation 40. As shown in FIG. 3, the docking station 30 has anindentation or aperture 41 that allows the base 38 of the stimulatorhousing 30 to be seated securely into the docking station. The connector36 of the stimulator housing is recessed in an aperture 37 of the baseof the stimulator housing 30 that may be covered by a detachable orhinged cover when the stimulator housing is not attached to the dockingstation (not shown).

The mated connectors 36 and 42 have a set of contacts that have specificfunctions for the transfer of power to charge a rechargable battery inthe stimulator housing 30 and to transfer data bidirectionally betweenthe stimulator housing and docking station. As a safety feature, thecontacts at the two ends of the mated connector are connected to oneanother within the stimulator housing and within the docking station,such that if physical connection is not made at those end contacts, allthe other contacts are disabled via active switches. Also, theconnectors 36 and 42 are offset from the center of the base 38 of thestimulator housing 30 and from the center of the indentation or aperture41 of the docking station 40, so that the stimulator housing can beinserted in only one way into the docking station. That is to say, whenthe stimulator housing 30 is attached to the docking station 40, thefront of the stimulator housing 30 must be on the front side of thedocking station 40. As shown, the back side of the docking station hasan on/off switch 44 and a power cord 43 that attaches to a wall outlet.The docking station 40 also has ports (e.g., USB ports) for connectingto other devices, one of which 45 is shown on the side of the station,and others of which are located on the front of the station (not shown).The front of the docking station has colored lights to indicatatewhether the docking station has not (red) or has (green) charged thestimulator so as to be ready for a stimulation session.

Through cables to the communication port 45, the docking station 40 cancommunicate with the different types of devices, such as thoseillustrated in FIG. 5. Handheld devices may resemble conventional remotecontrols with a display screen (FIG. 5A) or mobile phones (FIG. 5B).Other type of devices with which the docking station may communicate aretouchscreen devices (FIG. 5C) and laptop computers (FIG. 5D). Asdescribed below, such communication may also be performed wirelessly.

The communication connections between different components of thestimulator's controller are shown in FIG. 6, which is an expandedrepresentation of the control unit 330 in FIG. 2. Connection between thedocking station controller components 332 and components within thestimulator housing 331 is denoted in FIG. 6 as 334. For example, thatconnection is made when the stimulator housing is connected to thedocking station as described above. Connection between the dockingstation controller components 332 and devices 333 such as those shown inFIG. 5 (generally internet-based components) is denoted as 335.Connection between the components within the stimulator housing 331 anddevices 333 such as those shown in FIG. 5 (generally internet-basedcomponents) is denoted as 336. Different embodiments of the inventionmay lack one or more of the connections. For example, if the connectionbetween the stimulator housing and the devices 333 is only through thedocking station controller components, then in that embodiment of theinvention, only connections 334 and 335 would be present.

The connections 334, 335 and 336 in FIG. 6 may be wired or wireless. Forexample, if the controller component 333 is the mobile phone shown inFIG. 5B, the connection 335 to a docking stationport (45 in FIG. 3)could be made with a cable to the phone's own docking port. Similarly,if the controller component 333 is the laptop computer shown in FIG. 5D,the connection 335 to a docking stationport (45 in FIG. 3) could be madewith a cable to a USB port on the computer. However, the preferredconnections 334, 335, and 336 will be wireless.

Although infrared or ultrasound wireless control might be used tocommunicate between components of the controller, they are not preferredbecause of line-of-sight limitations. Instead, in the presentdisclosure, the communication between devices preferably makes use ofradio communication within unlicensed ISM frequency bands (260-470 MHz,902-928 MHz, 2400-2.4835 GHz). Components of a radio frequency system indevices 331, 332, and 333 typically comprise a system-on-chiptransciever with an integrated microcontroller; a crystal; associatedbalun & matching circuitry, and an antenna [Dag GRINI. R F Basics, R Ffor Non-RF Engineers. Texas Instruments, Post Office Box 655303, Dallas,Tex. 75265, 2006].

Transceivers based on 2.4 GHz offer high data rates (greater than 1Mbps) and a smaller antenna than those operating at lower frequencies,which makes them suitable for with short-range devices. Furthermore, a2.4 GHz wireless standard (Bluetooth, Wi-Fi, and ZigBee) may be used asthe protocol for transmission between devices. Although the ZigBeewireless standard operates at 2.4 GHz in most jurisdictions worldwide,it also operates in the ISM frequencies 868 MHz in Europe, and 915 MHzin the USA and Australia. Data transmission rates vary from 20 to 250kilobits/second with that standard.

FIG. 6 also shows that sensor devices that measure physiological andenvironmental signals may connect to the control unit 330 via any of itssubsystems (stimulator body 331, docking station 332, and handheld orinternet-based devices 333). Because many commercially availablehealth-related sensors may operate using ZigBee, its use may berecommended for applications in which the controller adjusts thepatient's vagus nerve stimulation based on the physiological sensors'values, as described in connection with FIG. 1 [ZigBee Wireless SensorApplications for Health, Wellness and Fitness. ZigBee Alliance 2400Camino Ramon Suite 375 San Ramon, Calif. 94583]. Systems for connectingsmartphones to physiologial sensors using Bluetooth may also be used.For example, BioZen, which is designed specifically for biofeedbackapplications, is based on the open source framework Bluetooth SensorProcessing for Android smartphones and is freely available. It mayconnect wirelessly to many commercially available physiological sensordevices [Anonymous. BIOZEN User's Manual. United States DefenseDepartment National Center for Telehealth and Technology. 9933 WestHayes Street, Joint Base Lewis-McChord, Wash. 98431, pp. 1-16, 2013].Commercially available wired and wireless physiological sensormeasurement devices using the e-Health Sensor Platform for Arduino andRaspberry Pi are also suitable for incorporation into, or connectionwith, the stimulator housing 30 or the docking station 40 in FIG. 3[Anonymous. e-Health Sensor Platform for Arduino and Raspberry Pi(Biometric/MedicalApplications). Technical literature from Cooking Hacks(the open hardware division of Libelium). Libelium ComunicacionesDistribuidas S. L., C/Maria de Luna 11, nave 17, C. P. 50018, Zaragoza,Spain. pp. 1-159, 2013]. Other such methods for incorporatingphysiological sensors into biofeedback systems have also been described[Guan-Zheng L I U, Bang-Yu Huang and Lei Wang. A Wearable RespiratoryBiofeedback System Based on Generalized Body Sensor Network.TELEMEDICINE and e-HEALTH 17(5,2011):348-357]. Use of such sensors isdescribed more completely below in a section on the use of biofeedbackand automatic control theory methods to improve treatment of individualpatients.

Application of the Stimulator to the Neck of the Patient

In different methodological embodiments of the present invention,selected nerve fibers are stimulated by the disclosed electricalstimulation devices. These methods include noninvasive stimulation at aparticular location on the patient's neck. Nerves stimulated at thatlocation comprise the vagus nerve, and in some embodiments, cutaneousnerve endings. At that location in the neck, the vagus nerve is situatedwithin the carotid sheath. The left vagus nerve is sometimes selectedfor stimulation, because stimulation of the right vagus nerve mayproduce undesired effects on the heart. However, depending on theapplication, the right vagus nerve or both right and left vagus nervesmay be stimulated instead.

To find the appropriate location to stimulate on the neck, the locationof the carotid sheath will first be ascertained by any method known inthe art, e.g., by feel and anatomical inference, or preferably byultrasound imaging [KNAPPERTZ V A, Tegeler C H, Hardin S J, McKinney WM. Vagus nerve imaging with ultrasound: anatomic and in vivo validation.Otolaryngol Head Neck Surg 118(1,1998):82-85; GIOVAGNORIO F andMartinoli C. Sonography of the cervical vagus nerve: normal appearanceand abnormal findings. AJR Am J Roentgenol 176(3,2001):745-749]. Thestimulator is then positioned at the level of about the fifth to sixthcervical vertebra.

FIG. 7 illustrates application of the device 30 shown in FIG. 3 to thepatient's neck, in order to stimulate the cervical vagus nerve on thatside of the neck. For reference, FIG. 7 shows the locations of thefollowing vertebrae: first cervical vertebra 71, the fifth cervicalvertebra 75, the sixth cervical vertebra 76, and the seventh cervicalvertebra 77.

FIG. 8 shows the stimulator 30 applied to the neck of a child, which ispartially immobilized with a foam cervical collar 78 that is similar toones used for neck injuries and neck pain. The collar is tightened witha strap 79, and the stimulator is inserted through a hole in the collarto reach the child's neck surface. As shown, the stimulator is turned onand off with a control knob, and the amplitude of stimulation may alsobe adjusted with the control knob that is located on the stimulator. Inother models, the control knob is absent or disabled, and the stimulatormay be turned on and off remotely, using a wireless controller (see FIG.5A) that may be used to adjust the stimulation parameters of thecontroller (e.g., on/off, stimulation amplitude, stimulation waveformfrequency, etc.).

FIGS. 9 and 10 illustrate some of the major structures of the neck, inorder to point out structures that could potentially be stimulatedelectrically, when the stimulator is positioned as in FIGS. 7 and 8. Forcomparison with FIG. 7, FIG. 9A illustrates the approximate locations ofthe cervical vertebrae C1 through C7. The thyroid cartilage, the largestof the cartilages that make up the cartilage structure in and around thetrachea that contains the larynx, lies at the vertebral levels of C4 andC5. The laryngeal prominence 111 (Adam's apple) in the middle of theneck is formed by the thyroid cartilage at approximately vertebral levelC4.

As shown in FIG. 9A, the common carotid artery 100 extends from the baseof the skull 102 through the neck 104 to the first rib and sternum (notshown). Carotid artery 100 includes an external carotid artery 106 andan internal carotid artery 108 and is protected by fibrous connectivetissue, namely, the carotid sheath. The three major structures withinthe carotid sheath are the common carotid artery 100, the internaljugular vein 110 and the vagus nerve (not shown).

Proceeding from the skin and fat of the neck to the carotid sheath, theshortest line from the stimulator 30 to the vagus nerve may passsuccessively through the platysma muscle 82, the sternocleidomastoidmuscle 65, and the carotid sheath (see FIGS. 9B and 9C). The anatomyalong this line is shown in more detail in FIG. 10, which is across-section of half of the neck at vertebra level C6. The vagus nerve60 is identified in FIG. 10, along with the carotid sheath 61 that isidentified there in bold peripheral outline. The carotid sheath enclosesnot only the vagus nerve, but also the internal jugular vein 62 and thecommon carotid artery 63. Structures that may be identified near thesurface of the neck include the external jugular vein 64 and thesternocleidomastoid muscle 65, which protrudes when the patient turnshis or her head. Additional organs in the vicinity of the vagus nerveinclude the trachea 66, thyroid gland 67, esophagus 68, scalenusanterior muscle 69, scalenus medius muscle 70, levator scapulae muscle71, splenius colli muscle 72, semispinalis capitis muscle 73,semispinalis colli muscle 74, longus colli muscle and longus capitismuscle 75. The sixth cervical vertebra 76 is shown with bony structureindicated by hatching marks. Additional structures shown in the figureare the phrenic nerve 77, sympathetic ganglion 78, brachial plexus 79,vertebral artery and vein 80, prevertebral fascia 81, platysma muscle82, omohyoid muscle 83, anterior jugular vein 84, sternohyoid muscle 85,sternothyroid muscle 86, and skin with associated fat 87.

The skin 87 at this location has innervation that is associated withparticular dermatomes, although the dermatome extent varies fromindividual to individual [LADAK A, Tubbs R S, Spinner R J. Mappingsensory nerve communications between peripheral nerve territories. ClinAnat. 2013 Jul. 3. doi: 10.1002/ca.22285, pp. 1-10; C. E. POLETTI. C2and C3 pain dermatomes in man. Cephalalgia 11(3,1991):155-159]. Men andwomen also have a different skin anatomy there because the skin of menmay contain a significantly greater number of hair follicles.

It is also understood that there may be significant individual variationin internal neck anatomy, and this should be taken into account whenpositioning the stimulator 30 [commonly assigned and co-pending patentapplication entitled IMPLANTATION OF WIRELESS VAGUS NERVE STIMULATORS,to SIMON et al., which is hereby incorporated by reference]. Inaddition, for patients having necks that are unusually wrinkled or thatcontain large amounts of fatty tissue, the skin may have to be firsttaped or otherwise made to conform to a flattened or smoothconfiguration in order for the methods of the invention to be appliedsuccessfully.

Once the stimulator has been preliminarily positioned, testing may beperformed in order to ascertain that the position is correct. Aftertesting, the correct position may be marked on the patient's skin, forexample with fluorescent dyes that are excited with infrared orultraviolet light, to facilitate subsequent placement of the stimulator[commonly assigned and co-pending patent application U.S. Ser. No.13/872,116, entitled DEVICES AND METHODS FOR MONITORING NON-INVASIVEVAGUS NERVE STIMULATION, to SIMON et al., which is hereby incorporatedby reference].

In certain aspects of the invention, the measurement of an evokedpotential may be used to optimize non-invasive stimulation of the vagusnerve with, for example, one of the devices described here. Given that aparticular evoked potential can be quantified that representsstimulation of the vagus nerve, the operator can use this measurement toconfirm that the action potentials have been created in the vagus nerveduring electrical stimulation. In this manner, the operator may, forexample, vary a characteristic of the electrical impulses generator bythe vagus nerve stimulator in order to ensure that such stimulation iseffectively stimulating the vagus nerve at a therapeutic level. Forexample, if such stimulation does not initially generate the evokedpotentials that would confirm the firing of the action potentials in thevagus nerve, the operator may vary aspects of the signal, such as theamplitude, frequency, pulse width and/or duty cycle until such an evokedpotential is generated. In addition or alternatively, the operator mayvary the placement or orientation of the device on the subject's neck toensure proper stimulation of the vagus nerve. As another alternative,the operator may position the vagal nerve stimulator on the other sideof the patient's neck (left to right or vice versa) in an attempt tooptimize the stimulation.

Use of Feedback and Automatic Control Theory Methods to Treat Patients

When vagus nerve stimulation is being performed, the disclosed systemgenerally also uses feedback methods, as defined in the engineeringcontrol theory of automatic control. For example, irrespective of theuse of biofeedback, feedback may be used in an attempt to compensate formotion of the stimulator relative to the vagus nerve and to avoidpotentially dangerous situations, such as excessive heart rate. It mayalso be used in a form of automatic gain control, in which theparameters of the vagus nerve stimulation are varied automatically untila responsive property, such as a characteristic of the evoked potential,lies within a preferred range.

Generally, the devices shown in FIG. 1B will be used to directlystimulate the vagus nerve, in addition to, or instead of, stimulatingsensory nerves within the skin. As described herein and in co-pending,commonly assigned patent application U.S. Ser. No. 13/222,087, entitledDevices and methods for non-invasive capacitive electrical stimulationand their use for vagus nerve stimulation on the neck of a patient, toSIMON et al. (which is hereby incorporated by reference), Applicant hasdeveloped a stimulator device that can noninvasively stimulate a vagusnerve directly in the patient's neck, without producing cutaneousdiscomfort to a patient. When the vagus nerve is being stimulated by thedevice, the quality of sensation in the patient's skin above the vagusnerve depends strongly on the stimulation current and frequency, suchthat when the currents are not much greater than the perceptionthreshold, the cutaneous sensations may be described as tingle, itch,vibration, buzz, touch, pressure, or pinch. For situations in which theskin is being stimulated with a constant current and with a particulartype of stimulation waveform that is described below, any such cutaneoussensation may be ignored by the patient, and the stimulator does notserve as an exteroceptive biofeedback device. In that case, the deviceresembles instead a physiological control device that may be used tostimulate structures of the central nervous system and/or “Otherphysiological systems”, via stimulation of the vagus nerve, as indicatedin FIG. 1B. The particular structures of the central nervous system orother physiological systems that are affected by the vagus nervestimulation depend on the parameters of the vagus nerve stimulation,which are selected to stimulate the particular system. Direct electricalstimulation of the vagus nerve will itself generate evoked potentials,as the resulting vagal action potentials and their sequelae propagatewithin the central nervous system.

FIG. 1B illustrates a closed-loop (feedback) system for producing (viasensory stimuli) and acquiring (via scalp electrodes) evoked potentialdata. As an example of such feedback methods, the vagus nerve stimulatormay vary a parameter of the nerve stimulus waveform (e.g. amplitude, orfrequency in the case of steady-state EP measurement), measure theresulting EP waveform, again vary the parameter based on that waveformmeasurement, and then repeat this procedure iteratively until it resultsin an EP waveform that exhibits preferred features that lie within somespecified range. As now described, with control theory methods, theparameters of the vagus nerve stimulation may be changed automatically,depending on the values on physiological measurements that are made (oron values of environmental signals such as ambient light and sound), inattempt to maintain the values of the physiological signals withinpredetermined ranges.

When stimulating the vagus nerve noninvasively, motion artifactvariability may often be attributable to the patient's breathing, whichinvolves contraction and associated change in geometry of thesternocleidomastoid muscle that is situated close to the vagus nerve(identified as 65 in FIGS. 9C and 10). Modulation of the stimulatoramplitude to compensate for this variability may be accomplished bymeasuring the patient's respiratory phase, or more directly by measuringmovement of the stimulator, then using controllers (e.g., PIDcontrollers) that are known in the art of control theory, as nowdescribed.

As shown in FIG. 1B, the central nervous system and physiologicalsystems receive input via a vagus nerve from the vagus nerve stimulationdevice, including the device's controlling electronic components thatmay be used to select or set parameters for the stimulation protocol(amplitude, frequency, pulse width, burst number, etc.) or alert thepatient as to the need to use or adjust the stimulator (i.e., an alarm).For example, the controller may comprise the control unit 330 in FIG. 2.Feedback to the controller in the schema shown in FIG. 1B is possiblebecause physiological measurements are made using sensors.

The physiological sensors used in the invention will ordinarily includemore sensors than those needed simply to construct a biofeedback signalfor a particular clinical application. This is because the extra sensorsmay be needed for purposes such as compensating for motion artifacts, orthey may be needed in order to properly model the time-course of thephysiological signal that is to be controlled, as described below.

The preferred sensors will include ones ordinarily used for ambulatorymonitoring. For example, the sensors may comprise those used inconventional Holter and bedside monitoring applications, for monitoringheart rate and variability, ECG, respiration depth and rate, coretemperature, hydration, blood pressure, brain function, oxygenation,skin impedance, and skin temperature. The sensors may be embedded ingarments or placed in sports wristwatches, as currently used in programsthat monitor the physiological status of soldiers [G. A. SHAW, A. M.Siegel, G. Zogbi, and T. P. Opar. Warfighter physiological andenvironmental monitoring: a study for the U.S. Army Research Institutein Environmental Medicine and the Soldier Systems Center. MIT LincolnLaboratory, Lexington Mass. 1 Nov. 2004, pp. 1-141]. The ECG sensorsshould be adapted to the automatic extraction and analysis of particularfeatures of the ECG, for example, indices of P-wave morphology, as wellas heart rate variability indices of parasympathetic and sympathetictone. Measurement of respiration using noninvasive inductiveplethysmography, mercury in silastic strain gauges or impedancepneumography is particularly advised, in order to account for theeffects of respiration on the heart. A noninvasive accelerometer mayalso be included among the ambulatory sensors, in order to identifymotion artifacts. An event marker may also be included in order for thepatient to mark relevant circumstances and sensations.

For brain monitoring, the sensors may comprise ambulatory EEG sensorsthat may also be used for measurement of evoked potentials [CASSON A,Yates D, Smith S, Duncan J, Rodriguez-Villegas E. Wearableelectroencephalography. What is it, why is it needed, and what does itentail? IEEE Eng Med Biol Mag. 29(3,2010):44-56] or optical topographysystems for mapping prefrontal cortex activation [ATSUMORI H, Kiguchi M,Obata A, Sato H, Katura T, Funane T, Maki A. Development of wearableoptical topography system for mapping the prefrontal cortex activation.Rev Sci Instrum. 2009 April; 80(4):043704, pp. 1-6]. Signal processingmethods, comprising not only the application of conventional linearfilters to the raw EEG data, but also the nearly real-time extraction ofnon-linear signal features from the data, may be considered to be a partof the EEG monitoring [D. Puthankattil SUBHA, Paul K. Joseph, RajendraAcharya U, and Choo Min Lim. EEG signal analysis: A survey. J Med Syst34(2010):195-212]. Such features would include EEG bands (e.g., delta,theta, alpha, beta).

Detection of the phase of respiration may be performed non-invasively byadhering a thermistor or thermocouple probe to the patient's cheek so asto position the probe at the nasal orifice. Strain gauge signals frombelts strapped around the chest, as well as inductive plethysmographyand impedance pneumography, are also used traditionally to generate asignal non-invasively that rises and falls as a function of the phase ofrespiration. Respiratory phase may also be inferred from movement of thesternocleidomastoid muscle that also causes movement of the vagus nervestimulator during breathing, measured using accelerometers attached tothe vagus nerve stimulator, as described below. After digitizing suchsignals, the phase of respiration may be determined using software suchas “puka”, which is part of PhysioToolkit, a large published library ofopen source software and user manuals that are used to process anddisplay a wide range of physiological signals [GOLDBERGER A L, AmaralLAN, Glass L, Hausdorff J M, Ivanov P Ch, Mark R G, Mietus J E, Moody GB, Peng C K, Stanley H E. PhysioBank, PhysioToolkit, and PhysioNet:Components of a New Research Resource for Complex Physiologic Signals.Circulation 101(23,2000):e215-e220] available from PhysioNet, M.I.T.Room E25-505A, 77 Massachusetts Avenue, Cambridge, Mass. 02139]. In oneembodiment of the present invention, the control unit 330 in FIG. 2contains an analog-to-digital converter to receive such analogrespiratory signals, and software for the analysis of the digitizedrespiratory waveform resides within the control unit 330. That softwareextracts turning points within the respiratory waveform, such asend-expiration and end-inspiration, and forecasts future turning-points,based upon the frequency with which waveforms from previous breathsmatch a partial waveform for the current breath. The control unit 330then controls the impulse generator 310 in FIG. 2, for example, tostimulate the selected nerve only during a selected phase ofrespiration, such as all of inspiration or only the first second ofinspiration, or only the expected middle half of inspiration. In otherembodiments of the invention, the physiological or environmental signalsare transmitted wirelessly to the controller, as shown in FIG. 6. Somesuch signals may be received by the docking station (e.g., ambient soundsignals) and other may be received within the stimulator housing (e.g.,motion signals).

It may be therapeutically advantageous to program the control unit 330in FIG. 2 to control the impulse generator 310 in such a way as totemporally modulate stimulation by the electrodes, depending on thephase of the patient's respiration. In patent applicationJP2008/081479A, entitled Vagus nerve stimulation system, to YOSHIHOTO, asystem is also described for keeping the heart rate within safe limits.When the heart rate is too high, that system stimulates a patient'svagus nerve, and when the heart rate is too low, that system tries toachieve stabilization of the heart rate by stimulating the heart itself,rather than use different parameters to stimulate the vagus nerve. Inthat disclosure, vagal stimulation uses an electrode, which is describedas either a surface electrode applied to the body surface or anelectrode introduced to the vicinity of the vagus nerve via a hypodermicneedle. That disclosure is unrelated to the biofeedback problems thatare addressed here, but it does consider stimulation during particularphases of the respiratory cycle, for the following reason. Because thevagus nerve is near the phrenic nerve (77 in FIG. 10), Yoshihotoindicates that the phrenic nerve will sometimes be electricallystimulated along with the vagus nerve. The present applicants have notexperienced this problem, so the problem may be one of a misplacedelectrode. In any case, the phrenic nerve controls muscular movement ofthe diaphragm, so consequently, stimulation of the phrenic nerve causesthe patient to hiccup or experience irregular movement of the diaphragm,or otherwise experience discomfort. To minimize the effects of irregulardiaphragm movement, Yoshihoto's system is designed to stimulate thephrenic nerve (and possibly co-stimulate the vagus nerve) only duringthe inspiration phase of the respiratory cycle and not duringexpiration. Furthermore, the system is designed to gradually increaseand then decrease the magnitude of the electrical stimulation duringinspiration (notably amplitude and stimulus rate) so as to makestimulation of the phrenic nerve and diaphragm gradual.

Furthermore, as an option in the present invention, parameters of thestimulation may be modulated by the control unit 330 to control theimpulse generator 310 in such a way as to temporally modulatestimulation by the electrodes, so as to achieve and maintain the heartrate within safe or desired limits. In that case, the parameters of thestimulation are individually raised or lowered in increments (power,frequency, etc.), and the effect as an increased, unchanged, ordecreased heart rate is stored in the memory of the control unit 330.When the heart rate changes to a value outside the specified range, thecontrol unit 330 automatically resets the parameters to values that hadbeen recorded to produce a heart rate within that range, or if no heartrate within that range has yet been achieved, it increases or decreasesparameter values in the direction that previously acquired data indicatewould change the heart rate in the direction towards a heart rate in thedesired range. Similarly, the arterial blood pressure is also recordednon-invasively in an embodiment of the invention (e.g., with a wristtonometer), and the control unit 330 extracts the systolic, diastolic,and mean arterial blood pressure from the blood pressure waveform. Thecontrol unit 330 will then control the impulse generator 310 in such away as to temporally modulate nerve stimulation by the electrodes, insuch a way as to achieve and maintain the blood pressure withinpredetermined safe or desired limits, by the same method that wasindicated above for the heart rate.

Let the measured output variables from physiological sensors of thesystem in FIG. 1B be denoted by y_(i) (i=1 to Q); let the desired(reference or setpoint) values of y_(i) be denoted by r_(i) and let thecontroller's output via the stimulator consist of variables u_(j) (j=1to P), which are also the input to the vagus nerve and other biologicalentities. The objective is for a controller to select the output fromthe stimulator, i.e. input to the body, (u_(j)) in such a way that thephysiological signal output variables (or a subset of them) closelyfollows the reference signals r_(i). Thus, it is intended that thecontrol error e_(i)=r_(i)−y_(i) be small, even if there is environmentalinput or noise to the system. In what follows, consider the errorfunction e_(i)=r_(i)−y_(i) to be the sensed physiological input to thecontrol unit 330 in FIG. 2 (i.e., the reference signals are integral tothe controller, which subtracts the measured system values from them toconstruct the control error signal). The controller will also receive aset of measured environmental signals v_(k) (k=1 to R), which also actupon the system as shown in FIG. 1B. The patient's response tobiofeedback may be considered to be a type of environmental input.During the initial, preliminary measurements, biofeedback is notperformed, but it may also be included during subsequent attempts totune and model the entire system.

As a first example of the use of feedback to control the system,consider the problem of adjusting the input u(t) to the body (i.e.,output from the controller as applied to the body via the impulsegenerator) in order to compensate for motion artifacts. Nerve activationis generally a function of the second spatial derivative of theextracellular potential along the nerve's axon, which would be changingas the position of the stimulator varies relative to the axon [F.RATTAY. The basic mechanism for the electrical stimulation of thenervous system. Neuroscience 89 (2, 1999):335-346]. Such motion artifactcan be due to movement by the patient (e.g., neck movement) or movementwithin the patient (e.g. sternocleidomastoid muscle contractionassociated with respiration), or it can be due to movement of thestimulator relative to the body (slippage or drift). Thus, one expectsthat because of such undesired or unavoidable motion, there will usuallybe some error (e=r−y) in the intended (r) versus actual (y) sensorvalues that needs continuous adjustment.

Accelerometers can be used to detect all these types of movement, usingfor example, Model LSM330DL from STMicroelectronics, 750 Canyon Dr #300Coppell, Tex. 75019. In one embodiment, one or more accelerometer isattached to the patient's neck, and one or more accelerometer isattached to the head(s) of the stimulator in the vicinity of where thestimulator contacts the patient. Because the temporally integratedoutputs of the accelerometers provide a measurement of the currentposition of each accelerometer, the combined accelerometer outputs makeit possible to measure any movement of the stimulator relative to theunderlying tissue.

The location of the vagus nerve underlying the stimulator may bedetermined preliminarily by placing an ultrasound probe at the locationwhere the center of the stimulator will be placed [KNAPPERTZ V A,Tegeler C H, Hardin S J, McKinney W M. Vagus nerve imaging withultrasound: anatomic and in vivo validation. Otolaryngol Head Neck Surg118(1,1998):82-5]. The ultrasound probe is configured to have the sameshape as the stimulator, including the attachment of one or moreaccelerometer. As part of the preliminary protocol, the patient withaccelerometers attached is then instructed or helped to perform neckmovements, breathe deeply so as to contract the sternocleidomastoidmuscle, and generally simulate possible motion that may accompanyprolonged stimulation with the stimulator. This would include possibleslippage or movement of the stimulator relative to an initial positionon the patient's neck. While these movements are being performed, theaccelerometers are acquiring position information, and the correspondinglocation of the vagus nerve is determined from the ultrasound image.With these preliminary data, it is then possible to infer the locationof the vagus nerve relative to the stimulator, given only theaccelerometer data during a stimulation session, by interpolatingbetween the previously acquired vagus nerve positional data as afunction of accelerometer position data.

For any given position of the stimulator relative to the vagus nerve, itis also possible to infer the amplitude of the electric field that itproduces in the vicinity of the vagus nerve. This is done by calculationor by measuring the electric field that is produced by the stimulator asa function of depth and position within a phantom that simulates therelevant bodily tissue [Francis Marion MOORE. Electrical Stimulation forpain suppression: mathematical and physical models. Thesis, School ofEngineering, Cornell University, 2007; Bartosz SAWICKI, Robert Szmurlo,Przemyslaw Plonecki, Jacek Starzyński, Stanislaw Wincenciak, AndrzejRysz. Mathematical Modelling of Vagus Nerve Stimulation. pp. 92-97 in:Krawczyk, A. Electromagnetic Field, Health and Environment: Proceedingsof EHE'07. Amsterdam, IOS Press, 2008]. Thus, in order to compensate formovement, the controller may increase or decrease the amplitude of theoutput from the stimulator (u) in proportion to the inferred deviationof the amplitude of the electric field in the vicinity of the vagusnerve, relative to its desired value.

A state-space representation, or model, of the entire system consists ofa set of first order differential equations of the form dy_(i)/dt=F_(i)(t,{y_(i)},{u_(j)},{v_(k)};{r_(j)}), where t is time andwhere in general, the rate of change of each variable y_(i) is afunction (F_(i)) of many other output variables as well as the input andenvironmental signals. Classical control theory is concerned withsituations in which the functional form of F_(i) is as a linearcombination of the state (y) and bodily input (u and v) variables, butin which coefficients of the linear terms are not necessarily known inadvance. In this linear case, the differential equations may be solvedwith linear transform (e.g., Laplace transform) methods, which convertthe differential equations into algebraic equations for straightforwardsolution. Thus, for example, a single-input single-output system(dropping the subscripts on variables) may have input from a controllerof the form: u(t)=K_(p)e(t)+K_(i)∫₀ ^(t)e(τ)dτ+K_(d)dr/de where theparameters for the controller are the proportional gain (K_(p)), theintegral gain (K_(i)) and the derivative gain (K_(d)). This type ofcontroller, which forms a controlling input signal with feedback usingthe error e=r−y, is known as a PID controller(proportional-integral-derivative). Commercial versions of PIDcontrollers are available, and they are used in 90% of all controlapplications.

Optimal selection of the parameters of the controller could be throughcalculation, if the coefficients of the corresponding state differentialequation were known in advance. However, they are ordinarily not known,so selection of the controller parameters (tuning) is accomplished byexperiments in which the error e either is or is not used to form thesystem input (respectively, closed loop or open loop experiments). In anopen loop experiment, the input is increased in a step (or random binarysequence of steps), and the system response is measured. In a closedloop experiment, the integral and derivative gains are set to zero, theproportional gain is increased until the system starts to oscillate, andthe period of oscillation is measured. Depending on whether theexperiment is open or closed loop, the selection of PID parameter valuesmay then be selected according to rules that were described initially byZiegler and Nichols. There are also many improved versions of tuningrules, including some that can be implemented automatically by thecontroller [LI, Y., Ang, K. H. and Chong, G. C. Y. Patents, software andhardware for PID control: an overview and analysis of the current art.IEEE Control Systems Magazine, 26 (1,2006): 42-54; Karl Johan Åström &Richard M. Murray. Feedback Systems: An Introduction for Scientists andEngineers. Princeton N.J.: Princeton University Press, 2008; FinnHAUGEN. Tuning of PID controllers (Chapter 10) In: Basic Dynamics andControl. 2009. ISBN 978-82-91748-13-9. TechTeach, Enggravhøgda 45,N-3711 Skien, Norway. http://techteach.no., pp. 129-155; Dingyu XUE,YangQuan Chen, Derek P. Atherton. PID controller design (Chapter 6), In:Linear Feedback Control: Analysis and Design with MATLAB. Society forIndustrial and Applied Mathematics (SIAM). 3600 Market Street, 6thFloor, Philadelphia, Pa. (2007), pp. 183-235; Jan JANTZEN, Tuning OfFuzzy PID Controllers, Technical University of Denmark, report 98-H 871,Sep. 30, 1998].

Although classical control theory works well for linear systems havingone or only a few system variables, special methods have been developedfor systems in which the system is nonlinear (i.e., the state-spacerepresentation contains nonlinear differential equations), or multipleinput/output variables. Such methods are important for the presentinvention because the physiological system to be controlled will begenerally nonlinear, and there will generally be multiple outputphysiological signals. It is understood that those methods may also beimplemented in the control unit 330 shown in FIG. 2 [Torkel GLAD andLennart Ljung. Control Theory. Multivariable and Nonlinear Methods. NewYork: Taylor and Francis, 2000; Zdzislaw BUBNICKI. Modern ControlTheory. Berlin: Springer, 2005].

The control unit 330 shown in FIG. 2 may also make use of feed-forwardmethods [Coleman BROSILOW, Babu Joseph. Feedforward Control (Chapter 9)In: Techniques of Model-Based Control. Upper Saddle River, N.J.:Prentice Hall PTR, 2002. pp, 221-240]. Thus, the controller in FIG. 2may be a type of predictive controller, methods for which have beendeveloped in other contexts as well, such as when a model of the systemis used to calculate future outputs of the system, with the objective ofchoosing among possible inputs so as to optimize a criterion that isbased on future values of the system's output variables.

A mathematical model of the system is needed in order to perform thepredictions of system behavior, for purposes of including thepredictions in a feedforward control device. If the mechanisms of thesystems are not sufficiently understood in order to construct aphysiologically-based model, a black-box model may be used instead. Suchmodels comprise autoregressive models [Tim BOLLERSLEV. Generalizedautoregressive conditional heteroskedasticity. Journal of Econometrics31(1986):307-327], or those that make use of principal components [JamesH. STOCK, Mark W. Watson. Forecasting with Many Predictors, In: Handbookof Economic Forecasting. Volume 1, G. Elliott, C. W. J. Granger and A.Timmermann, eds (2006) Amsterdam: Elsevier B. V, pp 515-554], Kalmanfilters [Eric A. WAN and Rudolph van der Merwe. The unscented Kalmanfilter for nonlinear estimation, In: Proceedings of Symposium 2000 onAdaptive Systems for Signal Processing, Communication and Control(AS-SPCC), IEEE, Lake Louise, Alberta, Canada, October, 2000, pp153-158], wavelet transforms [O. RENAUD, J.-L. Stark, F. Murtagh.Wavelet-based forecasting of short and long memory time series. SignalProcessing 48(1996):51-65], hidden Markov models [Sam ROWEIS and ZoubinGhahramani. A Unifying Review of Linear Gaussian Models. NeuralComputation 11(2,1999): 305-345], or artificial neural networks[Guoquiang ZHANG, B. Eddy Patuwo, Michael Y. Hu. Forecasting withartificial neural networks: the state of the art. International Journalof Forecasting 14(1998): 35-62].

For the present invention, the preferred black box model will be onethat makes use of support vector machines. A support vector machine(SVM) is an algorithmic approach to the problem of classification withinthe larger context of supervised learning. A number of classificationproblems whose solutions in the past have been solved by multi-layerback-propagation neural networks, or more complicated methods, have beenfound to be more easily solvable by SVMs. In the present context, atraining set of physiological data will have been acquired that includeswhether or not a physiological variable is outside of its desired range.Ordinarily, the variable will be one that is associated with thepatient's condition (e.g., blood pressure for a hypertensive individual,or when biofeedback is being performed it may be the physiologicalsignal used to construct the biofeedback signal).

Thus, the classification of the patient's state is whether or not thevariable is out of range, and the data used to make the classificationconsist of the remaining acquired physiological data, evaluated at Atime units prior to the time at which a forecast of the patient's statusis to be made. Accordingly, the SVM is trained to forecast Δ time unitsinto the future, where the time of the future forecast Δ is selected bythe user. The forecast consists of whether the variable is out of range,and optionally the predicted values of any or all of the physiologicalvariables that are being sensed. After training the SVM, it isimplemented as part of the controller. If Δ=0 and the signal beingforecast is the one use to construct a biofeedback signal, then thesignal is simply the ordinary biofeedback signal. However, when Δ>0, thesignal presented exteroceptively to the patient can correspond to apredicted, future value of the physiological variable. In that case, thesystem is effectively used for biofeedforward control, rather than forbiofeedback control. Then, the patient can learn to respond consciouslyto what the signal is predicted to become, rather than to what itcurrently is. Just as an anticipatory response is useful for muscularsystems such as when attempting to grasp a moving rather than stationaryobject, then so too, the biofeedforward control is useful for control ofthe autonomic nervous system when it is experiencing significanttime-varying fluctuations [Christopher J. C. BURGES. A tutorial onsupport vector machines for pattern recognition. Data Mining andKnowledge Discovery 2(1998), 121-167; J. A. K. Suykens, J. Vandewalle,B. De Moor. Optimal Control by Least Squares Support Vector Machines.Neural Networks 14 (2001):23-35; Sapankevych, N. and Sankar, R. TimeSeries Prediction Using Support Vector Machines: A Survey. IEEEComputational Intelligence Magazine 4(2,2009): 24-38; Press, W H;Teukolsky, S A; Vetterling, W T; Flannery, B P (2007). Section 16.5.Support Vector Machines. In: Numerical Recipes: The Art of ScientificComputing (3rd ed.). New York: Cambridge University Press].

A disclosure of the use of such feedback and feedforward methods toforecast and avert the onset of many types of medical crises was made inthe co-pending, commonly assigned patent application U.S. Ser. No.13/655,716 (publication US20130066395), entitled Nerve stimulationmethods for averting imminent onset or episode of a disease, to SIMON etal, which is hereby incorporated by reference. The medical crisescomprise attacks of migraine headache, as well as an asthma attack,epileptic seizure, transient ischemic attack or stroke, onset of atrialfibrillation, myocardial infarction, onset of ventricular fibrillationor tachycardia, panic attack, and attacks of acute depression. Thepresent invention extends that disclosure to allow the additional use ofbiofeedback, as shown in FIG. 1B.

An application of that previous disclosure, in the context of thepresent invention, is as follows. When the physiological system has beenmathematically modeled first without the use of biofeedback, the modelprovides an estimate of the temporal behavior of the system when it isfree from conscious control by the individual whose physiologicalproperties are being measured. When biofeedback is subsequentlyincorporated into the methods as shown in FIG. 1B, then to the extentthat the forecasted behavior of the physiological system deviates fromwhat the model predicts, that quantitative deviation may be attributedin part to how the individual is consciously trying to modulate thephysiological system. In the previous discussion surrounding FIG. 1B, itwas described how vagus nerve stimulation can be used to amplify orenhance the conscious control of the system, by first allowing theindividual to attempt biofeedback by itself, then using the device tosense the direction that the individual is trying to move thephysiological variable and amplify that effect by stimulating the vagusnerve to move the variable even more. The mathematical model of thesystem described above may be used for other situations, in which bothbiofeedback and automatic control are being performed simultaneously. Inthose cases, the intentions of the individual may be inferred from thedisclosed device as corresponding to the deviation of the physiologicalvariable from what the model predicts, taking into account the standarddeviation of the model's forecasting capabilities. The stimulator maythen be programmed to stimulate the vagus nerve in such a way as toamplify or enhance the inferred intentions of the individual, whenbiofeedback and automatic control are used simultaneously.

Selection of the Electrical Stimulation Waveform

In the present invention, electrical stimulation of the vagus nerveand/or the skin results secondarily in the stimulation of regions of thebrain that are involved in sensory processing, autonomic regulation andconscious action. Selection of stimulation waveform parameters topreferentially modulate particular regions of the brain may be doneempirically, wherein a set of electrical stimulation waveform parametersis chosen (amplitude, frequency, pulse width, etc.), and the responsiveregion of the brain is measured using fMRI or a related imaging method[CHAE J H, Nahas Z, Lomarev M, Denslow S, Lorberbaum J P, Bohning D E,George M S. A review of functional neuroimaging studies of vagus nervestimulation (VNS). J Psychiatr Res. 37(6,2003):443-455; CONWAY C R,Sheline Y I, Chibnall J T, George M S, Fletcher J W, Mintun M A.Cerebral blood flow changes during vagus nerve stimulation fordepression. Psychiatry Res. 146(2,2006):179-84]. Thus, by performing theimaging with different sets of stimulation parameters, a database may beconstructed, such that the inverse problem of selecting parameters tomatch a particular selected brain region may be solved by consulting thedatabase.

However, there may be significant variation between individuals inregards to the correspondence between stimulation parameters and theassociated brain structures that are activated. Furthermore, it may beimpractical to perform fMRI imaging on each individual who is to betrained or treated by the disclosed invention. The individualizedselection of parameters for the nerve stimulation protocol will in anycase involve some trial and error, in order to obtain a beneficialresponse without the sensation of skin pain or muscle twitches. Theparameters may also have to be updated periodically to compensate forany adaptation on the part of the patient's nervous system to theelectrical stimulation. In addition, the selection of parameter valuesmay involve tuning and modeling as understood in control theory, asdescribed in the previous section. It is also understood that to someextent, parameters may also be varied randomly in order to simulatenormal physiological variability, thereby possibly inducing a beneficialresponse in the patient [BUCHMAN T G. Nonlinear dynamics, complexsystems, and the pathobiology of critical illness. Curr Opin Crit Care10(5,2004):378-82].

With regard to stimulating the patient's skin to construct a biofeedbacksignal, many stimulation waveforms that have been tried in connectionwith electro-tactile communication devices may also be used for thepresent invention [R. H. GIBSON. Electrical stimulation of pain andtouch. pp. 223-261. In: D. R. Kenshalo, ed. The Skin Senses.Springfield, Ill.: Charles C Thomas, 1968; Erich A. PFEIFFER. Electricalstimulation of sensory nerves with skin electrodes for research,diagnosis, communication and behavioral conditioning: A survey. Medicaland Biological Engineering. 6(6,1968):637-651; Kahori KITA, KotaroTakeda, Rieko Osu, Sachiko Sakata, Yohei Otaka, Junichi Ushiba. ASensory feedback system utilizing cutaneous electrical stimulation forstroke patients with sensory loss. Proc. 2011 IEEE InternationalConference on Rehabilitation Robotics, Zurich, Switzerland, Jun. 29-Jul.1, 2011, 2011:5975489, pp 1-6; Mark R. PRAUSNITZ. The effects ofelectric current applied to skin: A review for transdermal drugdelivery. Advanced Drug Delivery Reviews 18 (1996) 395-425].

For example, let stimL be the lower threshold of the skin stimulationcurrent, defined for each patient as the lowest current at which he orshe can feel stimulation to the skin. Let stimU be the upper thresholdof the skin stimulation current, defined as a fixed percentage (e.g.95%) of the magnitude of current to the skin that first begins tomaterially stimulate the vagus nerve, as evidenced by any of the methodsdescribed in commonly assigned and co-pending patent application U.S.Ser. No. 13/872,116, entitled DEVICES AND METHODS FOR MONITORINGNON-INVASIVE VAGUS NERVE STIMULATION, to SIMON et al., which is herebyincorporated by reference. StimU may be measured when the waveform usedto stimulate the vagus nerve itself is simultaneously applied as asuperimposed signal (see below), but in which the vagus stimulationwaveform has an amplitude that is also set just under the one at whichthe vagus nerve is first materially stimulated.

Let ipL and ipU be the minimum and maximum values of the sensedphysiological variable that are to be used for biofeedback,respectively. Each of these factors (stimL, stimU, ipL and ipU) ismeasured or decided shortly prior to the therapy. Let stim(n) be definedas a magnification factor of the current at the n-th sampling of thephysiological signal that is used to construct the biofeedback signal,which then has the value ip(n). Then, let stim(n)=stimL when ip(n)<ipL;let stim(n)=stimU when ip(n)>ipU, and let stim(n) vary linearly betweenstimL and stimU as a function of ip(n), when ip(n) is between or at theendpoints ipL and ipU.

In this embodiment, the electrical biofeedback signal to the skin willbe proportional to stim(n) multiplied by f(t), where f(t) is amonophasic rectangular electric pulse sequence having a repeat intervalof, for example, 10 milliseconds and duration of 300 microseconds. Theinterval and pulse duration may be optimized for each patient, so thatthe psychological sensation of the cutaneous biofeedback is maximizedfor a given total skin current, but without any sensation of pain ordiscomfort.

A digital biofeedback signal to the skin may also be used. For example,ipL, ipU, and ipL+(ipU−ipL)/2 may be used as the only three levels thatare applied to the skin, and each of them may have a pulse trainduration of, e.g., 0.5, 1, or 2 seconds, for a total of 9 possiblesignal train combinations. The pulse train that is actually applied atany instant may then be selected according to the measured physiologicalsignal, with higher amplitude and longer pulse trains corresponding toincreasing values of the physiological signal.

The selection of a waveform to stimulate a nerve that lies deep underthe skin, such as a vagus nerve, is a more difficult problem because theselection must be made so as not to cause skin pain or muscle twitches.The waveform for stimulating the deep nerve will generally besuperimposed upon the cutaneous biofeedback signal described above. FIG.11A illustrates an exemplary electrical voltage/current profile for astimulating, blocking and/or modulating impulse applied to a portion orportions of selected nerve (e.g. vagus nerve) in accordance with anembodiment of the present invention. For the preferred embodiment, thevoltage and current refer to those that are non-invasively producedwithin the patient by the electrodes (or stimulator coils). As shown, asuitable electrical voltage/current profile 400 for the blocking and/ormodulating impulse 410 to the portion or portions of a nerve may beachieved using pulse generator 310 in FIG. 2. In a preferred embodiment,the pulse generator 310 may be implemented using a power source 320 anda control unit 330 having, for instance, a processor, a clock, a memory,etc., to produce a pulse train 420 to the electrodes 340 that deliverthe stimulating, blocking and/or modulating impulse 410 to the nerve.The parameters of the modulation signal 400, such as the frequency,amplitude, duty cycle, pulse width, pulse shape, etc., are preferablyprogrammable. An external communication device may modify the pulsegenerator programming to facilitate treatment.

A device such as that disclosed in patent publication No. US2005/0216062may be employed to generate the stimulation waveform. That patentpublication discloses a multifunctional electrical stimulation (ES)system adapted to yield output signals for effecting electromagnetic orother forms of electrical stimulation for a broad spectrum of differentbiological and biomedical applications, which produce an electric fieldpulse in order to non-invasively stimulate nerves. The system includesan ES signal stage having a selector coupled to a plurality of differentsignal generators, each producing a signal having a distinct shape, suchas a sine wave, a square or a saw-tooth wave, or simple or complexpulse, the parameters of which are adjustable in regard to amplitude,duration, repetition rate and other variables. Examples of the signalsthat may be generated by such a system are described in a publication byLIBOFF [A. R. LIBOFF. Signal shapes in electromagnetic therapies: aprimer. pp. 17-37 in: Bioelectromagnetic Medicine (Paul J. Rosch andMarko S. Markov, eds.). New York: Marcel Dekker (2004)]. The signal fromthe selected generator in the ES stage is fed to at least one outputstage where it is processed to produce a high or low voltage or currentoutput of a desired polarity whereby the output stage is capable ofyielding an electrical stimulation signal appropriate for its intendedapplication. Also included in the system is a measuring stage whichmeasures and displays the electrical stimulation signal operating on thesubstance being treated, as well as the outputs of various sensors whichsense prevailing conditions prevailing in this substance, whereby theuser of the system can manually adjust the signal, or have itautomatically adjusted by feedback, to provide an electrical stimulationsignal of whatever type the user wishes, who can then observe the effectof this signal on the entity being treated.

The stimulating and/or modulating impulse signal 410 in FIG. 11Apreferably has a frequency, an amplitude, a duty cycle, a pulse width, apulse shape, etc. selected to influence the therapeutic result, namely,stimulating and/or modulating some or all of the transmissions of theselected nerve. For example, the frequency may be about 1 Hz or greater,such as between about 15 Hz to 100 Hz, more preferably around 25 Hz. Themodulation signal may have a pulse width selected to influence thetherapeutic result, such as about 1 microseconds to about 1000microseconds. For example, the electric field induced or produced by thedevice within tissue in the vicinity of a nerve may be about 5 to 600V/m, preferably less than 100 V/m, and even more preferably less than 30V/m. The gradient of the electric field may be greater than 2 V/m/mm.More generally, the stimulation device produces an electric field in thevicinity of the nerve that is sufficient to cause the nerve todepolarize and reach a threshold for action potential propagation, whichis approximately 8 V/m at 1000 Hz. The modulation signal may have a peakvoltage amplitude selected to influence the therapeutic result, such asabout 0.2 volts or greater, such as about 0.2 volts to about 40 volts.

An objective of the disclosed stimulator is to provide both nerve fiberselectivity and spatial selectivity. Spatial selectivity may be achievedin part through the design of the electrode (or magnetic coil)configuration, and nerve fiber selectivity may be achieved in partthrough the design of the stimulus waveform, but designs for the twotypes of selectivity are intertwined. This is because, for example, awaveform may selectively stimulate only one of two nerves whether theylie close to one another or not, obviating the need to focus thestimulating signal onto only one of the nerves [GRILL W and Mortimer JT. Stimulus waveforms for selective neural stimulation. IEEE Eng. Med.Biol. 14 (1995): 375-385]. These methods complement others that are usedto achieve selective nerve stimulation, such as the use of localanesthetic, application of pressure, inducement of ischemia, cooling,use of ultrasound, graded increases in stimulus intensity, exploitingthe absolute refractory period of axons, and the application of stimulusblocks [John E. SWETT and Charles M. Bourassa. Electrical stimulation ofperipheral nerve. In: Electrical Stimulation Research Techniques,Michael M. Patterson and Raymond P. Kesner, eds. Academic Press. (NewYork, 1981) pp. 243-295].

To date, the selection of stimulation waveform parameters for vagusnerve stimulation has been highly empirical, in which the parameters arevaried about some initially successful set of parameters, in an effortto find an improved set of parameters for each patient. A more efficientapproach to selecting stimulation parameters might be to select astimulation waveform that mimics electrical activity in the anatomicalregions that one is attempting activate indirectly, in an effort toentrain the naturally occurring electrical waveform, as suggested inpatent number U.S. Pat. No. 6,234,953, entitled Electrotherapy deviceusing low frequency magnetic pulses, to THOMAS et al. and applicationnumber US20090299435, entitled Systems and methods for enhancing oraffecting neural stimulation efficiency and/or efficacy, to GLINER etal. One may also vary stimulation parameters iteratively, in search ofan optimal setting [U.S. Pat. No. 7,869,885, entitled Thresholdoptimization for tissue stimulation therapy, to BEGNAUD et al]. However,some stimulation waveforms, such as those described below, arediscovered by trial and error, and then deliberately improved upon.

Invasive nerve stimulation typically uses square wave pulse signals.However, Applicant found that square waveforms are not ideal fornon-invasive stimulation of the vagus nerve because they produceexcessive pain. Pre-pulses and similar waveform modifications have beensuggested as methods to improve selectivity of nerve stimulationwaveforms, but Applicant did not find them ideal [Aleksandra VUCKOVIC,Marco Tosato and Johannes J Struijk. A comparative study of threetechniques for diameter selective fiber activation in the vagal nerve:anodal block, depolarizing prepulses and slowly rising pulses. J. NeuralEng. 5 (2008): 275-286; Aleksandra VUCKOVIC, Nico J. M. Rijkhoff, andJohannes J. Struijk. Different Pulse Shapes to Obtain Small FiberSelective Activation by Anodal Blocking—A Simulation Study. IEEETransactions on Biomedical Engineering 51(5,2004):698-706; KristianHENNINGS. Selective Electrical Stimulation of Peripheral Nerve Fibers:Accommodation Based Methods. Ph.D. Thesis, Center for Sensory-MotorInteraction, Aalborg University, Aalborg, Denmark, 2004].

Applicant also found that stimulation waveforms consisting of bursts ofsquare pulses are not ideal for non-invasive stimulation [M. I. JOHNSON,C. H. Ashton, D. R. Bousfield and J. W. Thompson. Analgesic effects ofdifferent pulse patterns of transcutaneous electrical nerve stimulationon cold-induced pain in normal subjects. Journal of PsychosomaticResearch 35 (⅔, 1991):313-321; U.S. Pat. No. 7,734,340, entitledStimulation design for neuromodulation, to De Ridder]. However, burstsof sinusoidal pulses were determined to be a preferred stimulationwaveform, as shown in FIGS. 11B and 11C. As seen there, individualsinusoidal pulses have a period of tau, and a burst consists of N suchpulses. This is followed by a period with no signal (the inter-burstperiod). The pattern of a burst followed by silent inter-burst periodrepeats itself with a period of T. For example, the sinusoidal periodtau may be 200 microseconds; the number of pulses per burst may be N=5;and the whole pattern of burst followed by silent inter-burst period mayhave a period of T=40000 microseconds, which is comparable to 25 Hzstimulation (a much smaller value of T is shown in FIG. 11C to make thebursts discernable). When these exemplary values are used for T and tau,the waveform contains significant Fourier components at higherfrequencies ( 1/200 microseconds=5000/sec), as compared with thosecontained in transcutaneous nerve stimulation waveforms, as currentlypracticed.

Applicant is unaware of such a waveform having been used with vagusnerve stimulation, but a similar waveform has been used to stimulatemuscle as a means of increasing muscle strength in elite athletes.However, for the muscle strengthening application, the currents used(200 mA) may be very painful and two orders of magnitude larger thanwhat are disclosed herein. Furthermore, the signal used for musclestrengthening may be other than sinusoidal (e.g., triangular), and theparameters tau, N, and T may also be dissimilar from the valuesexemplified above [A. DELITTO, M. Brown, M. J. Strube, S. J. Rose, andR. C. Lehman. Electrical stimulation of the quadriceps femoris in anelite weight lifter: a single subject experiment. Int J Sports Med10(1989):187-191; Alex R WARD, Nataliya Shkuratova. Russian ElectricalStimulation: The Early Experiments. Physical Therapy 82 (10,2002):1019-1030; Yocheved LAUFER and Michal Elboim. Effect of Burst Frequencyand Duration of Kilohertz-Frequency Alternating Currents and ofLow-Frequency Pulsed Currents on Strength of Contraction, MuscleFatigue, and Perceived Discomfort. Physical Therapy 88(10,2008):1167-1176; Alex R WARD. Electrical Stimulation UsingKilohertz-Frequency Alternating Current. Physical Therapy 89(2,2009):181-190; J. PETROFSKY, M. Laymon, M. Prowse, S. Gunda, and J.Batt. The transfer of current through skin and muscle during electricalstimulation with sine, square, Russian and interferential waveforms.Journal of Medical Engineering and Technology 33 (2,2009): 170-181; U.S.Pat. No. 4,177,819, entitled Muscle stimulating apparatus, to KOFSKY etal]. Burst stimulation has also been disclosed in connection withimplantable pulse generators, but wherein the bursting is characteristicof the neuronal firing pattern itself [U.S. Pat. No. 7,734,340 to DERIDDER, entitled Stimulation design for neuromodulation; applicationUS20110184486 to DE RIDDER, entitled Combination of tonic and burststimulations to treat neurological disorders]. By way of example, theelectric field shown in FIGS. 11B and 11C may have an E_(max) value of17 V/m, which is sufficient to stimulate the nerve but is significantlylower than the threshold needed to stimulate surrounding muscle.

High frequency electrical stimulation is also known in the treatment ofback pain at the spine [Patent application US20120197369, entitledSelective high frequency spinal cord modulation for inhibiting pain withreduced side effects and associated systems and methods, to ALATARIS etal.; Adrian A L KAISY, Iris Smet, and Jean-Pierre Van Buyten. Analgeiaof axial low back pain with novel spinal neuromodulation. Posterpresentation #202 at the 2011 meeting of The American Academy of PainMedicine, held in National Harbor, Md., Mar. 24-27, 2011].

Those methods involve high-frequency modulation in the range of fromabout 1.5 KHz to about 50 KHz, which is applied to the patient's spinalcord region. However, such methods are different from the presentinvention because, for example, they is invasive; they do not involve abursting waveform, as in the present invention; they necessarily involveA-delta and C nerve fibers and the pain that those fibers produce (seebelow), whereas the present invention does not; they may involve aconduction block applied at the dorsal root level, whereas the presentinvention may stimulate action potentials without blocking of suchaction potentials; and/or they involve an increased ability of highfrequency modulation to penetrate through the cerebral spinal fluid,which is not relevant to the present invention. In fact, a likelyexplanation for the reduced back pain that is produced by their use offrequencies from 10 to 50 KHz is that the applied electrical stimulus atthose frequencies causes permanent damage to the pain-causing nerves,whereas the present invention involves only reversible effects [LEE R C,Zhang D, Hannig J. Biophysical injury mechanisms in electrical shocktrauma. Annu Rev Biomed Eng 2(2000):477-509].

Consider now which nerve fibers may be stimulated by the non-invasivevagus nerve stimulation waveform shown in FIGS. 11B and 11C. A vagusnerve in man consists of over 100,000 nerve fibers (axons), mostlyorganized into groups. The groups are contained within fascicles ofvarying sizes, which branch and converge along the nerve. Under normalphysiological conditions, each fiber conducts electrical impulses onlyin one direction, which is defined to be the orthodromic direction, andwhich is opposite the antidromic direction. However, external electricalstimulation of the nerve may produce action potentials that propagate inorthodromic and antidromic directions. Besides efferent output fibersthat convey signals to the various organs in the body from the centralnervous system, the vagus nerve conveys sensory (afferent) informationabout the state of the body's organs back to the central nervous system.Some 80-90% of the nerve fibers in the vagus nerve are afferent(sensory) nerves, communicating the state of the viscera to the centralnervous system.

The largest nerve fibers within a left or right vagus nerve areapproximately 20 μm in diameter and are heavily myelinated, whereas onlythe smallest nerve fibers of less than about 1 μm in diameter arecompletely unmyelinated. When the distal part of a nerve is electricallystimulated, a compound action potential may be recorded by an electrodelocated more proximally. A compound action potential contains severalpeaks or waves of activity that represent the summated response ofmultiple fibers having similar conduction velocities. The waves in acompound action potential represent different types of nerve fibers thatare classified into corresponding functional categories, withapproximate diameters as follows: A-alpha fibers (afferent or efferentfibers, 12-20 μm diameter), A-beta fibers (afferent or efferent fibers,5-12 μm), A-gamma fibers (efferent fibers, 3-7 μm), A-delta fibers(afferent fibers, 2-5 μm), B fibers (1-3 μm) and C fibers (unmyelinated,0.4-1.2 μm). The diameters of group A and group B fibers include thethickness of the myelin sheaths. It is understood that the anatomy ofthe vagus nerve is developing in newborns and infants, which accounts inpart for the maturation of autonomic reflexes. Accordingly, it is alsounderstood that the parameters of vagus nerve stimulation in the presentinvention are chosen in such a way as to account for this age-relatedmaturation [PEREYRA P M, Zhang W, Schmidt M, Becker LE. Development ofmyelinated and unmyelinated fibers of human vagus nerve during the firstyear of life. J Neural Sci 110(1-2, 1992):107-113].

The waveform disclosed in FIG. 11 contains significant Fouriercomponents at high frequencies (e.g., 1/200 microseconds=5000/sec), evenif the waveform also has components at lower frequencies (e.g., 25/sec).Transcutaneously, A-beta, A-delta, and C fibers are typically excited at2000 Hz, 250 Hz, and 5 Hz, respectively, i.e., the 2000 Hz stimulus isdescribed as being specific for measuring the response of A-beta fibers,the 250 Hz for A-delta fibers, and the 5 Hz for type C fibers [George D.BAQUIS et al. TECHNOLOGY REVIEW: THE NEUROMETER CURRENT PERCEPTIONTHRESHOLD (CPT). Muscle Nerve 22 (Supplement 8,1999): S247-S259].Therefore, the high frequency component of the noninvasive stimulationwaveform will preferentially stimulate the A-alpha and A-beta fibers,and the C fibers will be largely unstimulated.

However, the threshold for activation of fiber types also depends on theamplitude of the stimulation, and for a given stimulation frequency, thethreshold increases as the fiber size decreases. The threshold forgenerating an action potential in nerve fibers that are impaled withelectrodes is traditionally described by Lapicque or Weiss equations,which describe how together the width and amplitude of stimulus pulsesdetermine the threshold, along with parameters that characterize thefiber (the chronaxy and rheobase). For nerve fibers that are stimulatedby electric fields that are applied externally to the fiber, as is thecase here, characterizing the threshold as a function of pulse amplitudeand frequency is more complicated, which ordinarily involves thenumerical solution of model differential equations or a case-by-caseexperimental evaluation [David BOINAGROV, Jim Loudin and DanielPalanker. Strength-Duration Relationship for Extracellular NeuralStimulation: Numerical and Analytical Models. J Neurophysiol104(2010):2236-2248].

For example, REILLY describes a model (the spatially extended nonlinearnodal model or SENN model) that may be used to calculate minimumstimulus thresholds for nerve fibers having different diameters [J.Patrick REILLY. Electrical models for neural excitation studies. JohnsHopkins APL Technical Digest 9(1, 1988): 44-59]. According to REILLY'sanalysis, the minimum threshold for excitation of myelinated A fibers is6.2 V/m for a 20 μm diameter fiber, 12.3 V/m for a 10 μm fiber, and 24.6V/m for a 5 μm diameter fiber, assuming a pulse width that is within thecontemplated range of the present invention (1 ms). It is understoodthat these thresholds may differ slightly from those produced by thewaveform of the present invention as illustrated by REILLY's figures,for example, because the present invention prefers to use sinusoidalrather than square pulses. Thresholds for B and C fibers arerespectively 2 to 3 and 10 to 100 times greater than those for A fibers[Mark A. CASTORO, Paul B. Yoo, Juan G. Hincapie, Jason J. Hamann,Stephen B. Ruble, Patrick D. Wolf, Warren M. Grill. Excitationproperties of the right cervical vagus nerve in adult dogs. ExperimentalNeurology 227 (2011): 62-68]. If we assume an average A fiber thresholdof 15 V/m, then B fibers would have thresholds of 30 to 45 V/m and Cfibers would have thresholds of 150 to 1500 V/m. The present inventionproduces electric fields at the vagus nerve in the range of about 6 to100 V/m, which is therefore generally sufficient to excite allmyelinated A and B fibers, but not the unmyelinated C fibers. Incontrast, invasive vagus nerve stimulators that have been used for thetreatment of epilepsy have been reported to excite C fibers in somepatients [EVANS M S, Verma-Ahuja S, Naritoku D K, Espinosa J A.Intraoperative human vagus nerve compound action potentials. Acta NeurolScand 110(2004): 232-238].

It is understood that although devices of the present invention maystimulate A and B nerve fibers, in practice they may also be used so asnot to stimulate the A-delta) and B fibers. In particular, if thestimulator amplitude has been increased to the point at which unwantedside effects begin to occur, the operator of the device may simplyreduce the amplitude to avoid those effects. For example, vagal efferentfibers responsible for bronchoconstriction have been observed to haveconduction velocities in the range of those of B fibers. In thoseexperiments, bronchoconstriction was only produced when B fibers wereactivated, and became maximal before C fibers had been recruited [R. M.McALLEN and K. M. Spyer. Two types of vagal preganglionic motoneuronesprojecting to the heart and lungs. J. Physiol. 282(1978): 353-364].Because proper stimulation with the disclosed devices does not result inthe side-effect of bronchoconstriction, evidently thebronchoconstrictive B-fibers are possibly not being activated when theamplitude is properly set. Also, the absence of bradycardia orprolongation of PR interval suggests that cardiac efferent B-fibers arenot stimulated. Similarly, A-delta afferents may behave physiologicallylike C fibers. Because stimulation with the disclosed devices does notproduce nociceptive effects that would be produced by jugular A-deltafibers or C fibers, evidently the A-delta fibers may not be stimulatedwhen the amplitude is properly set.

The use of feedback to generate the modulation signal 400 in FIG. 11 mayresult in a signal that is not periodic, particularly if the feedback isproduced from sensors that measure naturally occurring, time-varyingaperiodic physiological signals from the patient (see FIG. 1B). In fact,the absence of significant fluctuation in naturally occurringphysiological signals from a patient is ordinarily considered to be anindication that the patient is in ill health. This is because apathological control system that regulates the patient's physiologicalvariables may have become trapped around only one of two or morepossible steady states and is therefore unable to respond normally toexternal and internal stresses. Accordingly, even if feedback were notused to generate the modulation signal 400, it may be useful toartificially modulate the signal in an aperiodic fashion, in such a wayas to simulate fluctuations that would occur naturally in a healthyindividual. Thus, the noisy modulation of the stimulation signal maycause a pathological physiological control system to be reset or undergoa non-linear phase transition, through a mechanism known as stochasticresonance [B. SUKI, A. Alencar, M. K. Sujeer, K. R. Lutchen, J. J.Collins, J. S. Andrade, E. P. Ingenito, S. Zapperi, H. E. Stanley,Life-support system benefits from noise, Nature 393 (1998) 127-128; WAlan C MUTCH, M Ruth Graham, Linda G Girling and John F Brewster.Fractal ventilation enhances respiratory sinus arrhythmia. RespiratoryResearch 2005, 6:41, pp. 1-9].

So, in one embodiment of the present invention, the modulation signal400 in FIG. 11, with or without feedback, will stimulate the selectednerve fibers in such a way that one or more of the stimulationparameters (power, frequency, and others mentioned herein) are varied bysampling a statistical distribution having a mean corresponding to aselected, or to a most recent running-averaged value of the parameter,and then setting the value of the parameter to the randomly sampledvalue. The sampled statistical distributions will comprise Gaussian and1/f, obtained from recorded naturally occurring random time series or bycalculated formula. Parameter values will be so changed periodically, orat time intervals that are themselves selected randomly by samplinganother statistical distribution, having a selected mean and coefficientof variation, where the sampled distributions comprise Gaussian andexponential, obtained from recorded naturally occurring random timeseries or by calculated formula.

Selection of Stimulation Parameters to Activate or Suppress SelectedNetworks of the Brain

FIG. 12 shows the location of the cervical stimulation as “Vagus NerveStimulation,” relative to its connections with other anatomicalstructures that are potentially affected by the stimulation. Indifferent embodiments of the invention, various brain and brainstemstructures are preferentially modulated by the stimulation. Besidesefferent output fibers that convey signals to the various organs in thebody from the central nervous system, the vagus nerve conveys sensory(afferent) information about the state of the body's organs back to thecentral nervous system. Propagation of electrical signals in efferentand afferent directions is indicated by arrows in FIG. 12. Ifcommunication between structures is bidirectional, this is shown in FIG.12 as a single connection with two arrows, rather than showing theefferent and afferent nerve fibers separately.

The vagus (or vagal) afferent nerve fibers arise from cell bodieslocated in the vagal sensory ganglia. These ganglia take the form ofswellings found in the cervical aspect of the vagus nerve just caudal tothe skull. There are two such ganglia, termed the inferior and superiorvagal ganglia. They are also called the nodose and jugular ganglia,respectively (See FIG. 12). The jugular (superior) ganglion is a smallganglion on the vagus nerve just as it passes through the jugularforamen at the base of the skull. The nodose (inferior) ganglion is aganglion on the vagus nerve located in the height of the transverseprocess of the first cervical vertebra.

Vagal afferents traverse the brainstem in the solitary tract, with someeighty percent of the terminating synapses being located in the nucleusof the tractus solitarius (or nucleus tractus solitarii, nucleus tractussolitarius, or NTS, see FIG. 12). The NTS projects to a wide variety ofstructures in the central nervous system, such as the amygdala, raphenuclei, periaqueductal gray, nucleus paragigantocellurlais, olfactorytubercule, locus ceruleus, nucleus ambiguus and the hypothalamus. TheNTS also projects to the parabrachial nucleus, which in turn projects tothe hypothalamus, the thalamus, the amygdala, the anterior insula, andinfralimbic cortex, lateral prefrontal cortex, and other corticalregions [JEAN A. The nucleus tractus solitarius: neuroanatomic,neurochemical and functional aspects. Arch Int Physiol Biochim Biophys99(5,1991):A3-A52]. Such central projections are discussed below inconnection with interoception and resting state neural networks.

With regard to vagal efferent nerve fibers, two vagal components haveevolved in the brainstem to regulate peripheral parasympatheticfunctions. The dorsal vagal complex, consisting of the dorsal motornucleus and its connections (see FIG. 12), controls parasympatheticfunction primarily below the level of the diaphragm (e.g. gut), whilethe ventral vagal complex, comprised of the nucleus ambiguus and nucleusretrofacial, controls functions primarily above the diaphragm in organssuch as the heart, thymus and lungs, as well as other glands and tissuesof the neck and upper chest, and specialized muscles such as those ofthe esophageal complex. For example, the cell bodies for thepreganglionic parasympathetic vagal neurons that innervate the heartreside in the nucleus ambiguus, which is relevant to potentialcardiovascular side effects that may be produced by vagus nervestimulation.

Non-invasive stimulation of the cervical vagus nerve (nVNS) is a noveltechnology for treating various central nervous system disorders,primarily by stimulating specific afferent fibers of the vagus nerve tomodulate brain function. This technology has been demonstrated in animaland human studies to treat a wide range of central nervous systemdisorders including headache (chronic and acute cluster and migraine),epilepsy, bronchoconstriction, anxiety disorders, depression, rhinitis,fibromyalgia, irritable bowel syndrome, stroke, traumatic brain injury,PTSD, Alzheimer's disease, autism, and others [See Cross Reference toRelated Applications for the corresponding co-pending and commonlyassigned applications, which are hereby incorporated by reference]. Manyof these conditions have also been treated with limited efficacy usingbiofeedback, and the combined use of biofeedback with vagus nervestimulation is intended to produce improved clinical results.

Applicants have discovered that as little as two-minutes of vagus nervestimulation produces effects that may last up to 8 hours or longer,depending on the type and severity of indication. Broadly speaking,there are three components to the effects of nVNS on the brain. Thestrongest effect occurs during the two minute stimulation and results insignificant changes in brain function that can be clearly seen as acutechanges in autonomic function (e.g. measured using pupillometry, heartrate variability, galvanic skin response, or evoked potential) andactivation and inhibition of various brain regions as shown in fMRIimaging studies. The second effect, of moderate intensity, lasts for 15to 180 minutes after stimulation. Animal studies have shown changes inneurotransmitter levels in various parts of the brain that persist forseveral hours. The third effect, of mild intensity, lasts up to 8 hoursand is responsible for the long lasting alleviation of symptoms seenclinically and, for example, in animal models of migraine headache.Thus, depending on the medical indication, whether it is a chronic oracute treatment, and the natural history of the disease, differenttreatment protocols may be used.

The vagus nerve stimulation may have excitatory and inhibitory effects.Some circuits involved in inhibition are illustrated in FIG. 12.Excitatory nerves within the dorsal vagal complex generally useglutamate as their neurotransmitter. To inhibit neurotransmission withinthe dorsal vagal complex, the present invention makes use of thebidirectional connections that the nucleus of the solitary tract (NTS)has with structures that produce inhibitory neurotransmitters, or itmakes use of connections that the NTS has with the hypothalamus, whichin turn projects to structures that produce inhibitoryneurotransmitters. The inhibition is produced as the result of thestimulation waveforms that are disclosed in the previous section. Thus,acting in opposition to glutamate-mediated activation by the NTS of thearea postrema and dorsal motor nucleus are: GABA, and/or serotonin,and/or norepinephrine from the periaqueductal gray, raphe nuclei, andlocus coeruleus, respectively. FIG. 12 shows how those excitatory andinhibitory influences combine to modulate the output of the dorsal motornucleus. Similar influences combine within the NTS itself, and thecombined inhibitory influences on the NTS and dorsal motor nucleusproduce a general inhibitory effect.

The activation of inhibitory circuits in the periaqueductal gray, raphenucei, and locus coeruleus by the hypothalamus or NTS may also causecircuits connecting each of these structures to modulate one another.Thus, the periaqueductal gray communicates with the raphe nuclei andwith the locus coeruleus, and the locus coeruleus communicates with theraphe nuclei, as shown in FIG. 12 [PUDOVKINA O L, Cremers T I, WesterinkB H. The interaction between the locus coeruleus and dorsal raphenucleus studied with dual-probe microdialysis. Eur J Pharmacol 7(2002);445(1-2):37-42.; REICHLING D B, Basbaum A I. Collateralization ofperiaqueductal gray neurons to forebrain or diencephalon and to themedullary nucleus raphe magnus in the rat. Neuroscience42(1,1991):183-200; BEHBEHANI M M. The role of acetylcholine in thefunction of the nucleus raphe magnus and in the interaction of thisnucleus with the periaqueductal gray. Brain Res 252(2,1982):299-307].The periaqueductal gray, raphe nucei, and locus coeruleus are also shownin FIG. 12 to project to many other sites within the brain.

The foregoing account of structures that are modulated by vagus nervestimulation is provided as background information needed to understandan embodiment of the invention in which vagus nerve stimulation is usedto modulate the activity of particular neural networks known as restingstate networks. A neural network in the brain is accompanied byoscillations within the network. Low frequency oscillations are likelyassociated with connectivity at the largest scale of the network, whilehigher frequencies are exhibited by smaller sub-networks within thelarger network, which may be modulated by activity in the sloweroscillating larger network. The default network, also called the defaultmode network (DMN), default state network, or task-negative network, isone such network that is characterized by coherent neuronal oscillationsat a rate lower than 0.1 Hz. Other large scale networks also have thisslow-wave property, as described below [BUCKNER R L, Andrews-Hanna J R,Schacter D L. The brain's default network: anatomy, function, andrelevance to disease. Ann N Y Acad Sci 1124(2008):1-38; PALVA J M, PalvaS. Infra-slow fluctuations in electrophysiological recordings,blood-oxygenation-level-dependent signals, and psychophysical timeseries. Neuroimage 62(4,2012):2201-2211; STEYN-ROSS M L, Steyn-Ross D A,Sleigh J W, Wilson M T. A mechanism for ultra-slow oscillations in thecortical default network. Bull Math Biol 73(2,2011):398-416].

The default mode network corresponds to task-independent introspection(e.g., daydreaming), or self-referential thought. When the DMN isactivated, the individual is ordinarily awake and alert, but the DMN mayalso be active during the early stages of sleep and during conscioussedation. During goal-oriented activity, the DMN is deactivated and oneor more of several other networks, so-called task-positive networks(TPN), are activated. DMN activity is attenuated rather thanextinguished during the transition between states, and is observed,albeit at lower levels, alongside task-specific activations. Strength ofthe DMN deactivation appears to be inversely related to the extent towhich the task is demanding. Thus, DMN has been described as atask-negative network, given the apparent antagonism between itsactivation and task performance. The posterior cingulate cortex (PCC)and adjacent precuneus and the medial prefrontal cortex (mPFC) are thetwo most clearly delineated regions within the DMN [RAICHLE M E, SnyderA Z. A default mode of brain function: a brief history of an evolvingidea. Neuroimage 37(4,2007):1083-1090; BROYD S J, Demanuele C, DebenerS, Helps S K, James C J, Sonuga-Barke E J. Default-mode braindysfunction in mental disorders: a systematic review. Neurosci BiobehavRev 33(3,2009):279-96; BUCKNER R L, Andrews-Hanna J R, Schacter D L. Thebrain's default network: anatomy, function, and relevance to disease.Ann N Y Acad Sci 1124(2008):1-38; BUCKNER R L, Sepulcre J, Talukdar T,Krienen F M, Liu H, Hedden T, Andrews-Hanna J R, Sperling R A, Johnson KA. Cortical hubs revealed by intrinsic functional connectivity: mapping,assessment of stability, and relation to Alzheimer's disease. J Neurosci29(2009):1860-1873; GREICIUS M D, Krasnow B, Reiss A L, Menon V.Functional connectivity in the resting brain: a network analysis of thedefault mode hypothesis. Proc Natl Acad Sci USA 100(2003): 253-258].

The term low frequency resting state networks (LFRSN or simply RSN) isused to describe both the task-positive and task-negative networks.Using independent component analysis (ICA) and related methods to assesscoherence of fMRI Blood Oxygenation Level Dependent Imaging (BOLD)signals in terms of temporal and spatial variation, as well asvariations between individuals, low frequency resting state networks inaddition to the DMN have been identified, corresponding to differenttasks or states of mind. They are related to their underlying anatomicalconnectivity and replay at rest the patterns of functional activationevoked by the behavioral tasks. That is to say, brain regions that arecommonly recruited during a task are anatomically connected and maintainin the resting state (in the absence of any stimulation) a significantdegree of temporal coherence in their spontaneous activity, which iswhat allows them to be identified at rest [SMITH S M, Fox P T, Miller KL, Glahn D C, Fox P M, et al. Correspondence of the brain's functionalarchitecture during activation and rest. Proc Natl Acad Sci USA106(2009): 13040-13045].

Frequently reported resting state networks (RSNs), in addition to thedefault mode network, include the sensorimotor RSN, the executivecontrol RSN, up to three visual RSNs, two lateralized fronto-parietalRSNs, the auditory RSN and the temporo-parietal RSN. However, differentinvestigators use different methods to identify the low frequencyresting state networks, so different numbers and somewhat differentidentities of RSNs are reported by different investigators [COLE D M,Smith S M, Beckmann CF. Advances and pitfalls in the analysis andinterpretation of resting-state FMRI data. Front Syst Neurosci4(2010):8, pp. 1-15]. Examples of RSNs are described in publicationscited by COLE and the following: ROSAZZA C, Minati L. Resting-statebrain networks: literature review and clinical applications. Neurol Sci32(5,2011):773-85; ZHANG D, Raichle M E. Disease and the brain's darkenergy. Nat Rev Neurol 6(1,2010):15-28; DAMOISEAUX, J. S., Rombouts, S.A. R. B., Barkhof, F., Scheltens, P., Stam, C. J., Smith, S. M.,Beckmann, C. F. Consistent resting-state networks across healthysubjects. Proc. Natl. Acad. Sci. U.S.A. 103(2006): 13848-13853 FOX M D,Snyder A Z, Vincent J L, Corbetta M, Van Essen D C, Raichle M E. Thehuman brain is intrinsically organized into dynamic, anticorrelatedfunctional networks. Proc Natl Acad Sci USA102(2005):9673-9678; LI R, WuX, Chen K, Fleisher A S, Reiman E M, Yao L. Alterations of DirectionalConnectivity among Resting-State Networks in Alzheimer Disease. AJNR AmJ Neuroradiol. 2012 Jul. 12. [Epub ahead of print, pp. 1-6].

For example, the dorsal attention network (DAN) and ventral attentionnetwork (VAN) are two networks responsible for attentional processing.The VAN is involved in involuntary actions and exhibits increasedactivity upon detection of salient targets, especially when they appearin unexpected locations (bottom-up activity, e.g. when an automobiledriver unexpectedly senses a hazard or unexpected situation). The DAN isinvolved in voluntary (top-down) orienting and increases activity afterpresentation of cues indicating where, when, or to what individualsshould direct their attention [FOX M D, Corbetta M, Snyder A Z, VincentJ L, Raichle M E. Spontaneous neuronal activity distinguishes humandorsal and ventral attention systems. Proc Natl Acad Sci USA103(2006):10046-10051; WEN X, Yao L, Liu Y, Ding M. Causal interactionsin attention networks predict behavioral performance. J Neurosci32(4,2012):1284-1292]. The DAN is bilaterally centered in theintraparietal sulcus and the frontal eye field. The VAN is largely rightlateralized in the temporal-parietal junction and the ventral frontalcortex. According to the present invention, it is generally desirable toactivate DAN by vagus nerve stimulation when biofeedback efforts are inprogress.

The attention systems (e.g., VAN and DAN) have been investigated longbefore their identification as resting state networks, and functionsattributed to the VAN have in the past been attributed to the locusceruleus/noradrenaline system [ASTON-JONES G, Cohen J D. An integrativetheory of locus coeruleus-norepinephrine function: adaptive gain andoptimal performance. Annu Rev Neurosci 28(2005):403-50; BOURET S, Sara SJ. Network reset: a simplified overarching theory of locus coeruleusnoradrenaline function. Trends Neurosci 28(11,2005):574-82; SARA S J,Bouret S. Orienting and Reorienting: The Locus Coeruleus MediatesCognition through Arousal. Neuron 76(1,2012):130-41; BERRIDGE C W,Waterhouse B D. The locus coeruleus-noradrenergic system: modulation ofbehavioral state and state-dependent cognitive processes. Brain ResBrain Res Rev 42(1,2003):33-84].

The attention systems originally described by PETERSON and Posner aremore expansive than just the VAN and DAN system, with interactinganatomical components corresponding to alerting, orienting, andexecutive control [PETERSEN S E, Posner M I. The attention system of thehuman brain: 20 years after. Annu Rev Neurosci 35(2012):73-89]. In thatdescription, DAN and VAN comprise significant portions of the orientingsystem, and components largely involving locus ceruleus-norepinephrinefunction comprise the alerting system. Other resting state networks areinvolved with executive control [BECKMANN C F, DeLuca M, Devlin J T,Smith S M. Investigations into resting-state connectivity usingindependent component analysis. Philos Trans R Soc Lond B Biol Sci360(1457,2005):1001-1013].

MENON and colleagues describe the anterior insula as being at the heartof the ventral attention system [ECKERT M A, Menon V, Walczak A,Ahlstrom J, Denslow S, Horwitz A, Dubno J R. At the heart of the ventralattention system: the right anterior insula. Hum Brain Mapp30(8,2009):2530-2541; MENON V, Uddin L Q. Saliency, switching, attentionand control: a network model of insula function. Brain Struct Funct214(5-6,2010):655-667]. However, SEELEY and colleagues usedregion-of-interest and independent component analyses of resting-statefMRI data to demonstrate the existence of an independent brain networkcomprised of both the anterior insula and dorsal ACC, along withsubcortical structures including the amygdala, substantia nigra/ventraltegmental area, and thalamus. This network is distinct from the otherwell-characterized large-scale brain networks, e.g. the default modenetwork [SEELEY W W, Menon V, Schatzberg A F, Keller J, Glover G H,Kenna H, et al. Dissociable intrinsic connectivity networks for salienceprocessing and executive control. J Neurosci 2007; 27(9):2349-2356].CAUDA and colleagues found that the human insula is functionallyinvolved in two distinct neural networks: i) the anterior pattern isrelated to the ventralmost anterior insula, and is connected to therostral anterior cingulate cortex, the middle and inferior frontalcortex, and the temporoparietal cortex; ii) the posterior pattern isassociated with the dorsal posterior insula, and is connected to thedorsal-posterior cingulate, sensorimotor, premotor, supplementary motor,temporal cortex, and to some occipital areas [CAUDA F, D'Agata F, SaccoK, Duca S, Geminiani G, Vercelli A. Functional connectivity of theinsula in the resting brain. Neuroimage 55(1,2011):8-23; CAUDA F,Vercelli A. How many clusters in the insular cortex? Cereb Cortex. 2012Sep. 30. (Epub ahead of print, pp. 1-2)]. TAYLOR and colleagues alsoreport two such resting networks [TAYLOR K S, Seminowicz D A, Davis K D.Two systems of resting state connectivity between the insula andcingulate cortex. Hum Brain Mapp 30(9,2009):2731-2745]. DEEN andcolleagues found three such resting state networks [DEEN B, Pitskel N B,Pelphrey K A. Three systems of insular functional connectivityidentified with cluster analysis. Cereb Cortex 21(7,2011):1498-1506].

Before disclosing methods for modulating resting state networks usingvagal nerve stimulation, we first discuss how stimulation of the vagusnerve can affect some of the relevant components of the brain, such asthe insula (see FIG. 12). These structures are involved in thehigher-level processing of sensory information. The sensory informationconsists not only of hearing, vision, taste & smell, and touch that maybe used as biofeedback modalities, but also other sensory modalitiessuch as proprioception, nociception and other forms of interoception.

For purposes of illustration in FIG. 12, we use interoceptive neuralpathways leading to the insula [CRAIG A D. How do you feel—now? Theanterior insula and human awareness. Nat Rev Neurosci 10(1,2009):59-70;BIELEFELDT K, Christianson J A, Davis B M. Basic and clinical aspects ofvisceral sensation: transmission in the CNS. Neurogastroenterol Motil17(4,2005):488-499; MAYER E A, Naliboff B D, Craig A D. Neuroimaging ofthe brain-gut axis: from basic understanding to treatment of functionalGI disorders. Gastroenterology 131(6,2006):1925-1942]. Anatomically,interoceptive sensations are distinguished from surface touch (tactile)sensations by their association with the spinothalamic projection thatascend in the contralateral spinal cord, rather than with the dorsalcolumn/medial lemniscal system which ascends the ipsilateral spinalcord. However, both contralateral and ipsilateral circuits are shown inthe spinal cord in FIG. 12 to indicate that the discussion applies moregenerally to sensory processing, not just the interoception. Inparticular, it applies to also to the circuits along which cutaneoussensations arising from electrical stimulation are propagated [A. ANGEL.Processing of sensory information. Progress in Neurobiology9(1977):1-122; G. WEDDELL and S. Miller. Cutaneous sensibility. AnnualReview of Physiology 24(1962):199-222]. This is indicated in FIG. 12 as“Sensors within the skin”, which are electrically stimulated as“Cutaneous stimulation.”

Interoceptive sensations arise from signals sent by parasympathetic andsympathetic afferent nerves. The latter are considered to be the primaryculprit for pain and other unpleasant emotional feelings, butparasympathetic afferents also contribute. Among afferents whose cellbodies are found in the dorsal root ganglia, the ones having type B cellbodies are most significant, which terminate in lamina I of the spinaland trigeminal dorsal horns. Other afferent nerves that terminate in thedeep dorsal horn provide signals related to mechanoreceptive,proprioceptive and nociceptive activity.

Lamina I neurons project to many locations. First, they project to thesympathetic regions in the intermediomedial and intermediolateral cellcolumns of the thoracolumbar cord, where the sympathetic preganglioniccells of the autonomic nervous system originate (See FIG. 12). Second,in the medulla, lamina I neurons project to the A1 catecholaminergiccell groups of the ventrolateral medulla and then to sites in therostral ventrolateral medulla (RVLM) which is interconnected with thesympathetic neurons that project to spinal levels. Only a limited numberof discrete regions within the supraspinal central nervous systemproject to sympathetic preganglionic neurons in the intermediolateralcolumn (see FIG. 12). The most important of these regions are therostral ventral lateral medulla (RVLM), the rostral ventromedial medulla(RVMM), the midline raphe, the paraventricular nucleus (PVN) of thehypothalamus, the medullocervical caudal pressor area (mCPA), and the A5cell group of the pons. The first four of these connections to theintermediolateral nucleus are shown in FIG. 12 [STRACK A M, Sawyer W B,Hughes J H, Platt K B, Loewy A D. A general pattern of CNS innervationof the sympathetic outflow demonstrated by transneuronal pseudorabiesviral infections. Brain Res. 491(1,1989): 156-162].

The rostral ventral lateral medulla (RVLM) is the primary regulator ofthe sympathetic nervous system, sending excitatory fibers(glutamatergic) to the sympathetic preganglionic neurons located in theintermediolateral nucleus of the spinal cord. Vagal afferents synapse inthe NTS, and their projections reach the RVLM via the caudalventrolateral medulla. However, resting sympathetic tone also comes fromsources above the pons, from hypothalamic nuclei, various hindbrain andmidbrain structures, as well as the forebrain and cerebellum, whichsynapse in the RVLM. Only the hypothalamic projection to the RVLM isshown in FIG. 12.

The RVLM shares its role as a primary regulator of the sympatheticnervous system with the rostral ventromedial medulla (RVMM) andmedullary raphe. Differences in function between the RVLM versusRVMM/medullary raphe have been elucidated for cardiovascular control,but are not well characterized for control of other organs such as thoseof the gut. Differential control of the RVLM by the hypothalamus mayalso occur via circulating hormones such as vasopressin. The RVMMcontains at least three populations of nitric oxide synthase neuronsthat send axons to innervate functionally similar sites in the NTS andnucleus ambiguus. Circuits connecting the RVMM and RVLM may besecondary, via the NTS and hypothalamus.

In the medulla, lamina I neurons also project another site, namely, tothe A2 cell group of the nucleus of the solitary tract, which alsoreceives direct parasympathetic (vagal and glossopharyngeal) afferentinput. As indicated above, the nucleus of the solitary tract projects tomany locations, including the parabrachial nucleus. In the pons andmesencephalon, lamina I neurons project to the periaqueductal grey(PAG), the main homeostatic brainstem motor site, and to theparabrachial nucleus. Sympathetic and parasympathetic afferent activityis integrated in the parabrachial nucleus. It in turn projects to theinsular cortex by way of the ventromedial thalamic nucleus (VMb, alsoknown as VPMpc). A direct projection from lamina I to the ventromedialnucleus (VMpo), and a direct projection from the nucleus tractussolitarius to the VMb, provide a rostrocaudally contiguous column thatrepresents all contralateral homeostatic afferent input. They projecttopographically to the mid/posterior dorsal insula (See FIG. 12).

In humans, this cortical image is re-represented in the anterior insulaon the same side of the brain. The parasympathetic activity isre-represented in the left (dominant) hemisphere, whereas thesympathetic activity is re-represented in the right (non-dominant)hemisphere. These re-representations provide the foundation for asubjective evaluation of interoceptive state, which is forwarded to theorbitofrontal cortex (See FIG. 12).

The right anterior insula is associated with subjective awareness ofhomeostatic emotions (e.g., visceral and somatic pain, temperature,sexual arousal, hunger, and thirst) as well as all emotions (e.g.,anger, fear, disgust, sadness, happiness, trust, love, empathy, socialexclusion). This region is intimately interconnected with the anteriorcingulate cortex (ACC). Unpleasant sensations are directly correlatedwith ACC activation [KLIT H, Finnerup N B, Jensen T S. Centralpost-stroke pain: clinical characteristics, pathophysiology, andmanagement. Lancet Neurol 8(9,2009):857-868]. The anterior cingulatecortex and insula are both strongly interconnected with theorbitofrontal cortex, amygdala, hypothalamus, and brainstem homeostaticregions, of which only a few connections are shown in FIG. 12.

Methods of the present invention comprise modulation of resting statenetworks containing or interacting with the insula using vagus nervestimulation. A first method directly targets the front end of theinteroceptive pathways shown in FIG. 12 (nucleus tractus solitarius,area postrema, and dorsal motor nucleus). The second method targets thedistal end of the interoceptive pathways (anterior insula and anteriorcingulate cortex).

According to the first method, electrical stimulation of A and B fibersalone of a vagus nerve causes increased inhibitory neurotransmitters inthe brainstem, which in turn inhibits signals sent to the parabrachialnucleus, VMb and VMpo. The stimulation uses special devices and aspecial waveform (described above), which minimize effects involving Cfibers that might produce unwanted side-effects. The electricalstimulation first affects the dorsal vagal complex, which is the majortermination site of vagal afferent nerve fibers. The dorsal vagalcomplex consists of the area postrema (AP), the nucleus of the solitarytract (NTS) and the dorsal motor nucleus of the vagus. The AP projectsto the NTS and dorsal motor nucleus of the vagus bilaterally. It alsoprojects bilaterally to the parabrachial nucleus and receives directafferent input from the vagus nerve. Thus, the area postrema is in aunique position to receive and modulate ascending interoceptiveinformation and to influence autonomic outflow [PRICE CJ, Hoyda T D,Ferguson A V. The area postrema: a brain monitor and integrator ofsystemic autonomic state. Neuroscientist 14(2,2008):182-194].

Projections to and from the locus ceruleus are particularly significantin the present invention because they are also used in the second methodthat is described below. The vagus nerve transmits information to thelocus ceruleus via the nucleus tractus solitarius (NTS), which has adirect projection to the dendritic region of the locus ceruleus. Otherafferents to, and efferents from, the locus ceruleus are described bySARA et al, SAMUELS et al, and ASTON-JONES [SARA S J, Bouret S.Orienting and Reorienting: The Locus Coeruleus Mediates Cognitionthrough Arousal. Neuron 76(1,2012):130-41; SAMUELS E R, Szabadi E.Functional neuroanatomy of the noradrenergic locus coeruleus: its rolesin the regulation of arousal and autonomic function part I: principlesof functional organization. Curr Neuropharmacol 6(3):235-53; SAMUELS, E.R., and Szabadi, E. Functional neuroanatomy of the noradrenergic locuscoeruleus: its roles in the regulation of arousal and autonomic functionpart II: physiological and pharmacological manipulations andpathological alterations of locus coeruleus activity in humans. Curr.Neuropharmacol. 6(2008), 254-285; Gary ASTON-JONES. Norepinephrine.Chapter 4 (pp. 47-57) in: Neuropsychopharmacology: The Fifth Generationof Progress (Kenneth L. Davis, Dennis Charney, Joseph T. Coyle, CharlesNemeroff, eds.) Philadelphia: Lippincott Williams & Wilkins, 2002].

In addition to the NTS, the locus ceruleus receives input from thenucleus gigantocellularis and its neighboring nucleusparagigantocellularis, the prepositus hypoglossal nucleus, theparaventricular nucleus of the hypothalamus, Barrington's nucleus, thecentral nucleus of the amygdala, and prefrontal areas of the cortex.These same nuclei receive input from the NTS, such that stimulation ofthe vagus nerve may modulate the locus ceruleus via the NTS and asubsequent relay through these structures.

The locus ceruleus has widespread projections throughout the cortex[SAMUELS E R, Szabadi E. Functional neuroanatomy of the noradrenergiclocus coeruleus: its roles in the regulation of arousal and autonomicfunction part I: principles of functional organization. CurrNeuropharmacol 6 (3):235-53]. It also projects to subcortical regions,notably the raphe nuclei, which release serotonin to the rest of thebrain. An increased dorsal raphe nucleus firing rate is thought to besecondary to an initial increased locus ceruleus firing rate from vagusnerve stimulation [Adrienne E. DORR and Guy Debonnelv. Effect of vagusnerve stimulation on serotonergic and noradrenergic transmission. JPharmacol Exp Ther 318(2,2006):890-898; MANTA S, Dong J, Debonnel G,Blier P. Enhancement of the function of rat serotonin and norepinephrineneurons by sustained vagus nerve stimulation. J Psychiatry Neurosci34(4,2009):272-80]. The locus ceruleus also has projections to autonomicnuclei, including the dorsal motor nucleus of the vagus, as shown inFIG. 1A [FUKUDA, A., Minami, T., Nabekura, J., Oomura, Y. The effects ofnoradrenaline on neurones in the rat dorsal motor nucleus of the vagus,in vitro. J. Physiol., 393 (1987): 213-231; MARTINEZ-PENA y Valenzuela,I., Rogers, R. C., Hermann, G. E., Travagli, R. A. (2004) Norepinephrineeffects on identified neurons of the rat dorsal motor nucleus of thevagus. Am. J. Physiol. Gas-trointest. Liver Physiol., 286, G333-G339;TERHORST, G. J., Toes, G. J., Van Willigen, J. D. Locus coeruleusprojections to the dorsal motor vagus nucleus in the rat. Neuroscience,45(1991): 153-160].

Selective Activation of Resting State Networks by Stimulation of theCervical Vagus Nerve

The above-mentioned circuits shown can be represented in terms offunctional resting state networks that may also contain variouscomponents that are shown in FIG. 12. A simplified representation ofthose networks is shown in FIG. 13. For purposes of discussion, we adoptthe set of resting state networks identified by LI et al, with theunderstanding that according to the above-cited publications, a more orless detailed set could also be adopted [LI R, Wu X, Chen K, Fleisher AS, Reiman E M, Yao L. Alterations of Directional Connectivity amongResting-State Networks in Alzheimer Disease. AJNR Am J Neuroradiol. 2012Jul. 12. [Epub ahead of print, pp. 1-6]. A similar set of resting statenetworks is described by DING et al [DING JR, Liao W, Zhang Z, MantiniD, Xu Q, Wu G R, Lu G, Chen H. Topological fractionation ofresting-state networks. PLoS One 6(10,2011):e26596, pp. 1-9]. FIG. 13also shows connections between the networks, with the larger arrowsindicating stronger connections. Solid and dashed arrows are,respectively, for positive and negative connections. According to thepresent invention, by activating particular resting state networks usingvagus nerve stimulation, one may preferentially generate evokedpotentials that correspond to those resting state networks, andconversely, confirm that particular resting state networks have beenactivated.

As described above, the dorsal attention network (DAN) and ventralattention network (VAN) are two networks responsible for attentionalprocessing. The VAN is involved in involuntary actions and exhibitsincreased activity upon detection of salient targets, especially whenthey appear in unexpected locations (bottom-up activity, e.g. when anautomobile driver unexpectedly senses a hazard). The DAN is involved involuntary (top-down) orienting and increases activity after presentationof cues indicating where, when, or to what individuals should directtheir attention [FOX M D, Corbetta M, Snyder A Z, Vincent J L, Raichle ME. Spontaneous neuronal activity distinguishes human dorsal and ventralattention systems. Proc Natl Acad Sci USA 103(2006):10046-10051; WEN X,Yao L, Liu Y, Ding M. Causal interactions in attention networks predictbehavioral performance. J Neurosci 32(4,2012):1284-1292]. The DAN isbilaterally centered in the intraparietal sulcus and the frontal eyefield. The VAN is largely right lateralized in the temporal-parietaljunction and the ventral frontal cortex.

The sensory-motor network (SMN) is the network covering thesomatosensory, premotor, and supplementary motor cortices. Cutaneousstimulation would preferentially activate the SMN, so the vagus nervestimulation may be directed to affect the SMN to enhance the cutaneoussignals. The lateral visual network (LVN) and medial visual network(MVN) are two networks for visual processing and are respectivelylocated in the lateral and medial parts of the visual cortex. Theauditory network (AN) is responsible for auditory processing and islocated in the bilateral superior temporal gyrus and in the primary andsecondary auditory cortices. The LVN, MVN, AN, and SMN are four networksrelated to sensory processing, and the DMN, SRN, DAN, and VAN areassociated with higher cognitive function.

The present invention modulates the activity of these resting statenetworks via the locus ceruleus by electrically stimulating the vagusnerve, as indicated in FIG. 13. Stimulation of a network by that routemay activate or deactivate a resting state network, depending on thedetailed configuration of adrenergic receptor subtypes within thenetwork and their roles in enhancing or depressing neural activitywithin the network, as well as subsequent network-to-networkinteractions.

According to the invention, one key to preferential stimulation of aparticular resting state network, such as those involving the insula, isto use a vagus nerve stimulation signal that entrains to the signatureEEG pattern of that network (see below and MANTINI D, Perrucci M G, DelGratta C, Romani G L, Corbetta M. Electrophysiological signatures ofresting state networks in the human brain. Proc Natl Acad Sci USA104(32,2007):13170-13175). By this EEG entrainment method, it may bepossible to preferentially activate, attenuate or deactivate particularnetworks, such as DAN or VAN. Activation of another network such as theSMN, VAN or DMN may also produce the same effect, via network-to-networkinteractions. Although the locus ceruleus is presumed to project to allof the resting networks, it is thought to project most strongly to theventral attention network (VAN) [CORBETTA M, Patel G, Shulman GL. Thereorienting system of the human brain: from environment to theory ofmind. Neuron 58(3,2008):306-24; MANTINI D, Corbetta M, Perrucci M G,Romani G L, Del Gratta C. Large-scale brain networks account forsustained and transient activity during target detection. Neuroimage44(1,2009):265-274]. Thus, deactivation of a particular network may alsobe attempted by activating another resting state network, because thebrain switches between them.

Stimulation waveforms may be constructed by superimposing or mixing theburst waveform shown in FIGS. 11B and 11C, in which each component ofthe mixture may have a different period T, effectively mixing differentburst-per-second waveforms. The relative amplitude of each component ofthe mixture may be chosen to have a weight according to correlations indifferent bands in an EEG for a particular resting state network. Thus,MANTINI et al performed simultaneous fMRI and EEG measurements and foundthat each resting state network has a particular EEG signature [see FIG.3 in: MANTINI D, Perrucci M G, Del Gratta C, Romani G L, Corbetta M.Electrophysiological signatures of resting state networks in the humanbrain. Proc Natl Acad Sci USA 104(32,2007):13170-13175]. They reportedrelative correlations in each of the following bands, for each restingstate network that was measured: delta (1-4 Hz), theta (4-8 Hz), alpha(8-13 Hz), beta (13-30 Hz), and gamma (30-50 Hz) rhythms. Forrecently-identified resting state networks, measurement of thecorresponding signature EEG networks will have to be performed.

According to the present embodiment of the invention, multiple signalsshown in FIGS. 11B and 11C are constructed, with periods T thatcorrespond to a location near the midpoint of each of the EEG bands(e.g., using the MINATI data, T equals approximately 0.4 sec, 0.1667sec, 0.095 sec, 0.0465 sec, and 0.025 sec, respectively). A morecomprehensive mixture could also be made by mixing more than one signalfor each band. These signals are then mixed, with relative amplitudescorresponding to the weights measured for any particular resting statenetwork, and the mixture is used to stimulate the vagus nerve of thepatient. Phases between the mixed signals are adjusted to optimize thefMRI signal for the resting state network that is being stimulated,thereby producing entrainment with the resting state network.Stimulation of a network may activate or deactivate a network, dependingon the detailed configuration of adrenergic receptors within the networkand their roles in enhancing or depressing neural activity within thenetwork, as well as subsequent network-to-network interactions. It isunderstood that variations of this method may be used when differentcombined fMRI-EEG procedures are employed and where the same restingstate may have different EEG signatures, depending on the circumstances[WU C W, Gu H, Lu H, Stein E A, Chen J H, Yang Y. Frequency specificityof functional connectivity in brain networks. Neuroimage42(3,2008):1047-1055; LAUFS H. Endogenous brain oscillations and relatednetworks detected by surface EEG-combined fMRI. Hum Brain Mapp29(7,2008):762-769; MUSSO F, Brinkmeyer J, Mobascher A, Warbrick T,Winterer G. Spontaneous brain activity and EEG microstates. A novelEEG/fMRI analysis approach to explore resting-state networks. Neuroimage52(4,2010):1149-1161; ESPOSITO F, Aragri A, Piccoli T, Tedeschi G,Goebel R, Di Salle F. Distributed analysis of simultaneous EEG-fMRItime-series: modeling and interpretation issues. Magn Reson Imaging27(8,2009):1120-1130; FREYER F, Becker R, Anami K, Curio G, VillringerA, Ritter P. Ultrahigh-frequency EEG during fMRI: pushing the limits ofimaging-artifact correction. Neuroimage 48(1,2009):94-108]. Once thenetwork is entrained, one may also attempt to change the signature EEGpattern of a network, by slowly changing the frequency content of thestimulation & EEG pattern of the network to which the stimulator isinitially entrained. An objective in this case would be to modify thefrequency content of the resting state signature EEG.

Protocols for Evoking Potentials by Stimulation of the Cervical VagusNerve

As described in connection with FIG. 1B, the present invention makes useof methods that have been described previously for stimulating andrecording visual, auditory, somatosensory, olfactory, gustatory, andvestibular evoked potentials [William R. GOFF. Human average evokedpotentials: procedures for stimulating and recording. Chapter 3, pp.101-156 in: Bioelectric Recording Techniques. Part B.Electroencephalography and Human Brain Potentials (Richard F. Thompsonand Michale M. Patterson, eds). New York: Academic Press, 1974; DavidREGAN. Human Brain Electrophysiology. Evoked potentials and evokedmagnetic fields in science and medicine. New York: Elsevier SciencePublishing Co., 1989, pp. 1-672; Terence W. PICTON, Otavio G. Lins andMichael Scherg. The recording and analysis of event-related potentials.Chapter 1 (pp. 3-73) in Handbook of Neuropsychology, Vol. 10 (F. Bollerand J. Grafman, eds). Amsterdam: Elsevier Science B.V., 1995; MonicaFABIANI, Gabriele Gratton and Michael G. H. Coles. Event RelatedPotentials. Methods, Theory, and Applications. Chapter 3, pp. 53-84 In:John T. Cacioppo, Louis G. Tassinary and Gary G. Berntson (eds).Handbook of Psychophysiology, 2nd Ed. Cambridge: Cambridge UniversityPress, 2000; Steven J. LUCK. An introduction to event-related potentialsand their neural origins. Chapter 1 (pp. 1-50) in: Steven J. LUCK. AnIntroduction to the Event-Related Potential Technique. Cambridge, Mass.:MIT Press, 2005; Todd C. HANDY (ed). Event-related Potentials: A MethodsHandbook. Camridge, Mass.: MIT Press, 2005, pp. 1-380; Steven J LUCK andEmily S Kappenman, eds. Oxford handbook of event-related potentialcomponents. Oxford: Oxford University Press, 2012, pp. 1-626]. Thus, astimulus for one or more of these senses may be generated by the deviceof the present invention (“Other Sensory Stimuli” in FIG. 1B), whichthen activates receptors for the corresponding sense(s) (“Other SenseOrgans” in FIG. 1B), and the resulting neuronal signal is thentransmitted to the central nervous system, for processing by brainstructures. The corresponding electrical currents within the brain aredetected as electrical potentials using electrodes on the scalp of thesubject, and those potentials are then recorded by data acquisitioncomponents of the system, as a function of time relative to thetime-of-onset of the sensory stimulus (see FIG. 1B).

If any of the above-mentioned senses is stimulated with a stimulushaving high enough intensity, the subject may sense the stimulus asbeing painful. However, if the activation of pain sensors is the primarysubject of the evoked potential investigation, the stimulus iscustomarily chosen to be a focused pulse of laser light [TREEDE R D,Lorenz J, Baumgärtner U. Clinical usefulness of laser-evoked potentials.Neurophysiol Clin 33(6,2003):303-314; GARCIA-LARREA L, Frot M, ValerianiM. Brain generators of laser-evoked potentials: from dipoles tofunctional significance; Neurophysiol Clin 33(6,2003):279-292]. In thepresent invention, the investigator may also stimulate the cervicalcutaneous sense receptors with an electrical current that evokes pain onthe part of the subject (see FIG. 1B). In fact, in preliminaryexperiments, the investigator will ordinarily increase the electricalcurrent arising from the vagus nerve stimulator in such a way as toascertain the range of currents (and stimulation voltages) that firstreach a sensory threshold and that eventually first produce a painfulsensation in the skin on the neck of the patient.

Ordinarily, the sensory stimuli that are applied in order to evokepotentials correspond to exteroceptive sense organs. However, thestimulation of interoceptive receptors may result in the generation ofevoked potentials as well, which has been investigated primarily bystimulating gastrointestinal interoceptors that can result in thesensation of internal pain [SARKAR S, Hobson A R, Furlong P L, Woolf CJ, Thompson D G, Aziz Q. Central neural mechanisms mediating humanvisceral hypersensitivity. Am J Physiol Gastrointest Liver Physiol281(5,2001):G1196-G1202]. Such evoked potentials are relevant to thepresent invention because gastrointestinal sensory information may betransmitted by branches of the vagus nerve [TOUGAS G, Hudoba P,Fitzpatrick D, Hunt R H, Upton A R. Cerebral evoked potential responsesfollowing direct vagal and esophageal electrical stimulation in humans.American Journal of Physiology 264(3 Pt 1,1993):G486-G491]. However, acaveat is that the evoked potential latencies observed in suchexperiments are extremely long and are considered to be responsesinduced by polysynaptic neural transmission, not directly reflectingascending conduction of the vagus nerve [USAMI K, Kawai K, Sonoo M,Saito N. Scalp-recorded evoked potentials as a marker for afferent nerveimpulse in clinical vagus nerve stimulation. Brain Stimul6(4,2013):615-623].

Vagus nerve stimulation has also been used in other attempts to evokepotentials that are measured with scalp electrodes. In the earliestinvestigations, the potentials that were purportedly evoked by invasivevagus nerve stimulation were determined to be artifacts involving thestimulation of muscle, which are generated in the region of thestimulating electrodes in the neck area [HAMMOND E J, Uthman B M, Reid SA, Wilder B J. Electrophysiologic studies of cervical vagus nervestimulation in humans: II. Evoked potentials. Epilepsia33(6,1992):1021-1028]. Evoked potentials were also described in U.S.Pat. No. 8,150,508 and U.S. Pat. No. 8,280,505, both entitled Vagusnerve stimulation method, to CRAIG, and U.S. Pat. No. 8,615,309,entitled Microburst electrical stimulation of cranial nerves for thetreatment of medical conditions, to CRAIG. However, those patentspertain only to the production of evoked potentials through stimulationof a nerve with an implanted nerve stimulator, and they did not disclosethe approximate latencies of purported evoked potentials, which couldarise artificially through the stimulation of muscle as described above.These considerations apply also to U.S. Pat. No. 7,801,601, entitledControlling neuromodulation using stimulus modalities, to MASCHINO etal.

In other investigations, a branch of the vagus nerve was electricallystimulated at the tragus of the ear, and evoked potentials werepurportedly measured [FALLGATTER A J, Neuhauser B, Herrmann M J, EhlisA-C, Wagener A, Scheuerpflug P, Reiners K and Riederer P. Far fieldpotentials from the brain stem after transcutaneus vagus nervestimulation. J Neural Transm 110(2003):1437-1443; FALLGATTER A J, EhlisA-C, Ringel T M, Herrmann M J. Age effect on far field potentials fromthe brain stem after transcutaneus vagus nerve stimulation. Int JPsychophysiol 56(2005):37-43; POLAK T, Ehlis A C, Langer J B M, PlichtaM M, Metzger F, Ringel T M, and Fallgatter A J. Noninvasive measurementof vagus activity in the brain stem—a methodological progress towardsearlier diagnosis of dementias? J Neural Transm 114(2007):613-619; POLAKT, Markulin F, Ehlis A-C, Langer J B M, Ringel T M, Fallgatter A J. Farfield potentials from brain stem after transcutaneous vagus nervestimulation: optimization of stimulation and recording parameters. JNeural Transm 116(2009):1237-1242]. However, those evoked potentialshave also been shown to be artifacts involving the stimulation of muscle[B. LEUTZOW, Lange J, Gibb A, Schroeder H, Nowak A, Wendt M, Usichenko TI. Vagal Sensory Evoked Potentials Disappear Under the NeuromuscularBlock—An Experimental Study. Brain Stimul 6(5,2013):812-816].

Other investigators have attempted to detect changes in EEG waveformsfollowing vagus nerve stimulation, but measurement of the EEG waveformwas not time-locked to the nerve stimulation, as would be required forthe measurement of an evoked potential. The acute or chronic effects ofvagus nerve stimulation on surface EEG waveforms is difficult to detectanyway [Michael BEWERNITZ, Georges Ghacibeh, Onur Seref, Panos M.Pardalos, Chang-Chia Liu, and Basim Uthman. Quantification of the impactof vagus nerve stimulation parameters on electroencephalographicmeasures. AIP Conf. Proc. DATA MINING, SYSTEMS ANALYSIS AND OPTIMIZATIONIN BIOMEDICINE; Nov. 5, 2007, Volume 953, pp. 206-219; Michael AndrewBEWERNITZ. Data mining and time series analysis of brain dynamicalbehavior with applications in epilepsy. PhD. Dissertation. Gainesville,Fla.: University of Florida. 2008. pp: 1-246]. However, such effects mayexist nevertheless, although they too might be the artificial result ofmuscle stimulation [KOO B. EEG changes with vagus nerve stimulation. JClin Neurophysiol. 18(5,2001):434-41; KUBA R, Guzaninová M, Brázdil M,Novák Z, Chrastina J, Rektor I. Effect of vagal nerve stimulation oninterictal epileptiform discharges: a scalp EEG study. Epilepsia.43(10,2002):1181-8; RIZZO P, Beelke M, De Carli F, Canovaro P, Nobili L,Robert A, Fornaro P, Tanganelli P, Regesta G, Ferrillo F. Modificationsof sleep EEG induced by chronic vagus nerve stimulation in patientsaffected by refractory epilepsy. Clin Neurophysiol. 115(3,2004):658-664;Zhaoyang CHEN, Hongwei Hao, Luming Li, Jie Dong. Wavelet Transform forRabbit EEG with Vagus Nerve Electric Stimulation. Proceedings of the28th IEEE EMBS Annual International Conference New York City, USA, Aug.30-Sep. 3, 2006 pp. 1715-1718].

Recently, USAMI and colleagues tried once again to measure credible,non-artifactual potentials that are evoked by the invasive, directstimulation of the cervical vagus nerve [USAMI K, Kawai K, Sonoo M,Saito N. Scalp-recorded evoked potentials as a marker for afferent nerveimpulse in clinical vagus nerve stimulation. Brain Stimul6(4,2013):615-623]. They determined that some of the early latency peaksand troughs in the evoked potential waveform actually had their originin currents within the central nervous system, as evidenced by the factthat they do not disappear upon the administration of muscle relaxant tothe subject. Applicants also performed the cervical vagus nervestimulation experiment that was reported by USAMI, except that in ourexperiments, the cervical vagus nerve was stimulated noninvasively usingelectrodes positioned on the subject's neck. We measured the location ofpeaks and troughs in the potentials that were evoked by the noninvasivevagus nerve stimulation and found that they were similar to those of thepeaks and troughs that had been determined to be non-artifactual byUSAMI et al. The results are shown in FIG. 14A, which displays thevoltages that were measured with scalp electrodes, as a function of timesince the onset of the electrical stimulus. The latency extrema areidentified there with the labels P1, N1, and P2 as in FIG. 1 of USAMI etal. The latencies were also found to be similar to those described byUSAMI et al. Thus, whereas the P1, N1, and P2 peak or trough latenciesin FIG. 14A were found at 3.1, 5.3, and 16.7 msec, respectively, theones described by USAMI et al. were measured to be 2.8, 3.6, and 11.3msec, respectively. These relatively small differences may be attributedto the fact that our vagus nerve stimulation was noninvasive, whereastheirs was invasive, as well as to differences in the stimulationcurrents in the vicinity the vagus nerve itself, and to differences inevoked potential waveforms between individuals.

The similarity between the evoked potentials that we measured, versusthose measured by USAMI et al, are evidence that our noninvasive vagusnerve stimulation experiments did in fact produce evoked potentials thatresult from action potentials that we generated in the cervical vagusnerve. An alternate explanation for the evoked potentials that wemeasured is that they were evoked by the stimulation of cutaneousreceptors that lie between the surface of the skin and the cervicalvagus nerve. However, that explanation is not likely because evokedpotentials that are produced by the electrical stimulation of cutaneousreceptors have latencies that are considerably different than the P1,N1, and P2 latency values that are shown in FIG. 14A [SLIMP J C, RubnerD E, Snowden M L, Stolov W C. Dermatomal somatosensory evokedpotentials: cervical, thoracic, and lumbosacral levels.Electroencephalogr Clin Neurophysiol 84(1,1992):55-70; KRAMER J K,Taylor P, Steeves J D, Curt A. Dermatomal somatosensory evokedpotentials and electrical perception thresholds during recovery fromcervical spinal cord injury. Neurorehabil Neural Repair24(4,2010):309-317]. Furthermore, when the noninvasive stimulatorelectrodes were displaced slightly from the positions used to producethe data shown in FIG. 14A, the evoked potential waveform was measuredinstead to be what is shown in FIG. 14B, which is dissimilar to what isshown in FIG. 14A. Thus, the evoked potential shown in FIG. 14B is notlikely to be due to the stimulation of the vagus nerve, but is likelyevoked by stimulation of receptors in the skin and/or muscle that aresituated near the vagus nerve.

Given that a particular evoked potential can be quantified thatrepresents stimulation of the vagus nerve, the operator can use thismeasurement to confirm that action potentials have been created in thevagus nerve during electrical stimulation. In this manner, the operatormay, for example, vary a characteristic of the electrical impulsesgenerator by the vagus nerve stimulator in order to ensure that suchstimulation is effectively stimulating the vagus nerve at a therapeuticlevel. For example, if such stimulation does not initially generate theevoked potentials that would confirm the firing of the action potentialsin the vagus nerve, the operator may vary aspects of the signal, such asthe amplitude, frequency, pulse width and/or duty cycle until such anevoked potential is generated. In addition or alternatively, theoperator may vary the placement or orientation of the device on thesubject's neck to ensure proper stimulation of the vagus nerve. Asanother alternative, the operator may position the vagus nervestimulator onto the other side of the patient's neck (left to right orvice versa) in an attempt to optimize the stimulation. Note that thepresent methods for optimizing the position of the vagus nervestimulation electrodes are different from the ones disclosed in U.S.Pat. No. 8,412,338, entitled Devices and methods for optimizingelectrode placement for anti-inflammatory stimulation, to FALTYS. TheFALTYS patent is concerned with positioning of the electrode based onthe appearance of stimulation artifacts, which he defines as a signal orsignals resulting from the electrode that is not part of the desiredstimulation. In contrast, the present disclosure is concerned with thepositioning of the electrode based on the appearance in an evokedpotential waveform of a feature that is thought NOT to be a stimulationartifact.

One application of direct vagus nerve stimulation at the neck is tomodulate neurotransmitter levels within the central nervous system ofpatients with certain medical disorders such as primary headache (e.g.,migraine), or fibromyalgia, who have a demonstrable habituation deficitwith regard to their evoked potentials. Thus, the patient may be tested(without feedback or biofeedback) by stimulating “other sense organs” orthe cervical cutaneous senses in FIG. 1B, and measuring thecorresponding evoked potentials, over an extended period of time (e.g.,visual, auditory, or traditional somatosensory EPs, as reviewed inCOPPOLA G, Pierelli F, Schoenen J. Habituation and migraine. NeurobiolLearn Mem 92(2,2009):249-259). The patients who do not exhibitsignificant habituation in their evoked potentials, in response to thesensory stimulation over a prolonged period of time, are then subjectedto an acute direct stimulation of the vagus nerve. The patient is thenretested (again without feedback or biofeedback) by stimulating “othersense organs” and re-measuring the previously-measured evoked potentials(visual, auditory, or traditional somatosensory EPs). For some of theindividuals (the “responders”), the effect of the intervening acutevagus nerve stimulation is to significantly reduce the magnitude offeatures of evoked potentials, thereby artificially effecting a form ofEP habituation. Those individuals are therefore candidates for chronictreatment of their migraine headaches, by performing the vagus nervestimulation on a regular basis, with the objective of reducing theduration, frequency and severity of symptoms associated with thedisorder (e.g., migraine attacks, pain associated with fibromyalgia,etc.). Methods for doing so were disclosed in the co-pending, commonlyassigned patent application U.S. Ser. No. 13/109,250, entitledElectrical and magnetic stimulators used to treat migraine/sinusheadache and comorbid disorders, to SIMON et al, and U.S. Ser. No.13/183,721 entitled Electrical and magnetic stimulators used to treatmigraine/sinus headache, rhinitis, sinusitis, rhinosinusitis, andcomorbid disorders, to SIMON et al. On the other hand, some individuals(the “non-responders”) may exhibit no significant changes to themagnitude of features of their evoked potentials following acutestimulation of their vagus nerve. It may be decided on the basis of thisoutcome that the “non-responders” are candidates for treatment bymethods other than performing vagus nerve stimulation on a regular basis[OZKUL Y, Bozlar S. Effects of fluoxetine on habituation of patternreversal visually evoked potentials in migraine prophylaxis. Headache42(7,2002):582-587].

Vagus nerve stimulation may also be useful for the treatment of patientsirrespective of whether the patient exhibits a deficit in thehabituation of evoked potentials, and irrespective of whether the vagusnerve stimulation promotes the normalization of habituation of evokedpotentials. In migraineurs, for example, the likely usefulness of thevagus nerve stimulation may more generally be based primarily upon thebaseline characteristics of an evoked potential, measured during one ormore phases of the migraine headache, particularly during the interictalphase. In fact, it is preferable to perform the measurements duringmultiple times throughout the interictal phase, in view of the changesin the evoked potential that occur throughout that phase. A method forusing previously measured values of characteristics of the baselineevoked potential, to infer the likelihood of therapeutic success, is asfollows. If the migraine attack is in progress, noninvasive vagus nervestimulation is administered, and its effect on the reduction of headachepain is measured. The pain measurement may be based on self-reporting ofthe patient, or it may be based on an objective physiologicalmeasurement of pain. Note that evoked potentials themselves may becorrelated with the level of pain and that EEG and autonomicphysiological variables collectively (heart rate variability,electrodermal response) may also be measured as being correlated withthe level of pain [LI D, Puntillo K, Miaskowski C. A review of objectivepain measures for use with critical care adult patients unable toself-report. J Pain 9(2008): 2-10; TOUSIGNANT-Laflamme Y, Rainville P,Marchand S. Establishing a link between heart rate and pain in healthysubjects: a gender effect. J Pain 6(2005): 341-347; NIR R R, Sinai A,Raz E, Sprecher E, Yarnitsky D. Pain assessment by continuous EEG:association between subjective perception of tonic pain and peakfrequency of alpha oscillations during stimulation and at rest. BrainRes 1344(2010): 77-86; Tor D. WAGER, Lauren Y. Atlas, Martin A.Lindquist, Mathieu Roy, Choong-Wan Woo and Ethan Kross. An fMRI-BasedNeurologic Signature of Physical Pain. N Engl J Med368(2013):1388-1397].

The measurement of pain may also be made following stimulation withmultiple sets of vagus nerve stimulation parameters, in order toevaluate the stimulation parameters that have the greatest effect on thereduction of pain. After vagus nerve stimulation, the evoked potentialmay be measured again, and the features of the baseline evoked potentialmay then be compared with features of the post-stimulation evokedpotential. Changes in the evoked potential may involve differences inamplitudes and latencies of peaks and troughs, which are of potentialpredictive value. When such measurements are performed on populations ofmigraineurs and control normal individuals, statistical methods may thenbe used to determine which features of the pre- and post-stimulationevoked potentials, as well as their differences, are most closelyrelated to the reduction of pain in the migraineur. The statisticalmethods may also be used to predict which parameters of the vagus nervestimulation have the greatest effect on the reduction of pain and on thefeatures of the pre- and post-stimulation evoked potentials. The vagusnerve stimulation may then be re-applied to the patient, with adifferent set of stimulation parameters, selected on the basis of therelation between those parameters and pain reduction, as well as oncharacteristics of the pre- and/or post-stimulation evoked potentials.

The vagus nerve stimulation may also be used as a prophylaxis to reducethe frequency or severity of migraine attacks. In that case, the vagusnerve stimulation is applied to the patient over a prolonged period oftime, and its quantitative effects on the frequency and severity of themigraine attacks is measured. When such measurements are performed onpopulations of migraineurs and control normal individuals, statisticalmethods may then be used to determine which features of the initial pre-and post-stimulation evoked potentials, as well as their differences,are most closely related to reduction in the chronic frequency andseverity of migraine attacks. Thereafter, the likelihood that vagusnerve stimulation will be successful in treating a migraineurchronically may be inferred from the measured features of his/herinitial pre- and post-stimulation evoked potentials, as well asdifferences between the pre- and post-stimulation evoked potentials.

Biofeedback Stimulation Protocols

As discussed above in connection with FIG. 1B, devices and methodsaccording to the present invention may involve combined biofeedback andautomatic control mechanisms, which begin with measurement ofphysiological properties of the individual using sensors. One suchphysiological property is the evoked potential, measured using scalpelectrodes. The present invention also contemplates the measurement andprocessing of many other types of physiological signals, including allof those that have been used in conventional biofeedback experiments.The following are the physiological signals that are nowadays ordinarilyused for biofeedback: the EEG (also measured using scalp electrodes, butnot time-locked to a stimulus as in an evoked potential measurement),the electromyogram (EMG), the electrodermal response, hand temperaturemeasurements; heart rate variability; and fMRI image features. The useof these and other biofeedback modalities was described in a co-pending,commonly assigned application, entitled Closed-loop, autonomic methodsof biofeedback using non-invasive vagus nerve stimulation, to SIMON etal.

In some situations, the relevant features of the evoked potentials maybe generated primarily by the central nervous system structures that areinvolved in conscious neural processing and control. As an example ofthat situation, the individual may consciously react to the sensationsthat result from the vagus nerve stimulation, as evidenced by theappearance of a P300 peak in his/her transient evoked potential. Afterdetecting the P300 peak, the device can use that fact to vary theparameters of the next vagus nerve stimulation. For example, the P300peak may appear once the stimulation amplitude reaches a sensorythreshold that is recognized by the subject, or the properties of theP300 peak may change when the stimulation amplitude is so large that itproduces pain.

The system shown in FIG. 1B may also be used to train an individual toconsciously and voluntarily control the “other physiological system”that is labeled in the figure. In such a biofeedback application, theskin at the subject's neck is stimulated in proportion to a previous orconcurrently measured property of the “other physiological system”(e.g., electrodermal voltage measured on the subject's hand), such thatthe subject is made consciously aware of the magnitude of the measuredphysiological property through the magnitude of the skin stimulation.Alternatively, the stimulation applied to the subject's neck is afunction of the features of the measured evoked potential (e.g.,amplitude or latency of one or more particular EP waveform peaks ortroughs). The subject then attempts to mentally control the magnitude ofthe skin stimulation, and thereby consciously control the magnitude ofthe measured physiological property through thought alone. Theelectrical signals that simulate cutaneous nerves within the skin may beanalog signals that vary in some continuous way relative to thephysiological property that is being transduced. Alternatively, thebiofeedback signals may be digital, comprising recognizable coded pulsetrains, as has been suggested in connection with tactile communicationdevices for the blind. For example, electrocutaneous signals with threediscrete intensity levels and three discrete long-pulse durations can bediscriminated [R. H. GIBSON. Electrical stimulation of pain and touch.pp. 223-261. In: D. R. Kenshalo, ed. The Skin Senses. Springfield, Ill.:Charles C Thomas, 1968; Erich A. PFEIFFER. Electrical stimulation ofsensory nerves with skin electrodes for research, diagnosis,communication and behavioral conditioning: A survey. Medical andBiological Engineering. 6(6,1968):637-651; Alejandro HERNANDEZ-ARIETA,Hiroshi Yokoi, Takashi Ohnishi, Tamio Arai. An f-MRI study of an EMGProsthetic Hand Biofeedback System. In: T. Arai et al. (Eds.). IAS-9,Proceedings of the 9th International Conference on IntelligentAutonomous Systems, University of Tokyo, Tokyo, Japan, Mar. 7-9, 2006,Amsterdam: IOS Press, 2006, pp. 921-929; Kahori KITA, Kotaro Takeda,Rieko Osu, Sachiko Sakata, Yohei Otaka, Junichi Ushiba. A Sensoryfeedback system utilizing cutaneous electrical stimulation for strokepatients with sensory loss. Proc. 2011 IEEE International Conference onRehabilitation Robotics, Zurich, Switzerland, Jun. 29-Jul. 1, 2011,2011:5975489, pp 1-6].

Methods for treating and training a patient according to the presentinvention comprise stimulating the vagus nerve as indicated in FIGS. 1B,7 and 8, using the electrical stimulation devices and stimulationwaveforms that are disclosed here, such as those in FIG. 11. Stimulationmay be performed on the left or right vagus nerve, or on both of themsimultaneously or alternately. The position and angular orientation ofthe device are adjusted at the preferred location on the neck, above thevagus nerve, until the patient perceives stimulation when current ispassed through the stimulator electrodes. The applied current isincreased gradually, first to a level wherein the patient feelssensation from the stimulation. The power is then increased, but is setto a level that is less than one at which the patient first indicatesany discomfort. The correctness of the location of the stimulator on thepatient's neck may be verified by any of the methods disclosed in theco-pending, commonly assigned application U.S. Ser. No. 13/872,116,entitled DEVICES AND METHODS FOR MONITORING NON-INVASIVE VAGUS NERVESTIMULATION, to SIMON et al., which is incorporated by reference].Straps, harnesses, or frames may then be used to maintain the stimulatorin position (see FIG. 8).

Physiological sensors will have been attached to the patient, and thecorresponding physiological measurements will then be made continuously,as described above. Ordinarily, one of those physiological signals willbe used to construct a biofeedback signal that is applied electricallyto the skin of the patient's neck. The appropriate range of thatelectrocutaneous biofeedback signal will then be determined as describedin the section above entitled “Selection of the electrical stimulationwaveform,” with the vagus nerve stimulation reduced to an amplitude thatis not sufficient to materially stimulate the vagus nerve. Otherbiofeedback signal modalities could be used too, such as an audio orvisual biofeedback signal, but they are not used in the basic invention.

At this point, the patient will attempt to use biofeedback to modify therelevant physiological signal, or will be trained to do so. For example,the physiological signal could be an electrodermal sensor for measuringgalvanic skin response, a thermometer for measuring finger temperatureand the associated blood flow, or an EEG-derived signal. Strategies forvoluntarily modulating the biofeedback signal include deliberatelyentering a particular emotional state or relaxing muscles. The inventionis intended to work with any of the biofeedback signals that have beendescribed in literature that is cited herein, and the intendedbiomedical applications of such published biofeedback methods apply aswell to the present invention.

According to one view, individuals who learn to perform biofeedback doso through a type of neural natural selection, in which pre-existing,randomly-activated efferent neural circuit paths are consciouslyselected, and the pool of possible circuit paths is measured by theperson-to-person lability of the corresponding physiological variable.According to this view, an individual with little lability will have fewcircuit paths from which to select, and will therefore be disadvantagedin terms of his or her potential to learn biofeedback skills. That is tosay, by measuring the natural, unprovoked physiological variability inthe physiological signal that is used for biofeedback, i.e., themagnitude of apparent “noise” in the signal about a baseline, one mightbe able to infer the likelihood that the individual will be able tolearn to perform biofeedback [R. Sergio GUGLIELMI and Alan H. Roberts.Volitional vasomotor lability and vasomotor control. BiologicalPsychology 39(1994):29-44].

This view is sometimes referred to as an efferent or so-called“feedforward” mechanism of biofeedback learning. Note that use of theterm “feedforward” in this sense refers to the efferent direction andhas nothing to do with the above-mentioned use of the term “feedforward”in engineering control theory. According to the present invention, ifthe vagus nerve is even stimulated with a sequence of randomly selectedstimulation parameters so as to indirectly and artificially increase thelability of the physiological signal, this alone may increase thelikelihood that the patient may learn to perform biofeedback [Thomas G.DUNN, Scott E. Gillig, Sharon E. Ponsor, Nolan Weil, and Sharon WilliamsUtz. The learning process in biofeedback: is it feedforward or feedback?Biofeedback and Self-Regulation 11(2,1986):143-156; Sharon Williams UTZ.The effect of instructions on cognitive strategies and performance inbiofeedback. Journal of Behavioral Medicine 17(3, 1994):291-308; J. M.LACROIX. The acquisition of autonomic control through biofeedback: thecase against an afferent process and a two-process alternative.Psychophysiology 18(5,1981):573-587].

An alternate, and not mutually exclusive, view of biofeedback learningis that the acquisition of voluntary visceral control is dependent uponthe ability to perceive or discriminate changes in visceral function.According to this view, biofeedback enhances discrimination ofinteroceptive events by providing additional exteroceptive cues. Thus,the individual must learn to discriminate interoceptive cues related tothe target response and to develop skills so as to attain control of theresponse, including possibly the development of new sensory abilitiesduring the training process. This view of biofeedback learning issometimes known as an “afferent” mechanism, to distinguish it from the“efferent” mechanism described in the previous paragraph.

The present invention provides another mechanism whereby suchdiscrimination can occur. Instead of, or in addition to, providing theadditional exeroceptive cues, the present invention is novel in that itprovides additional interoceptive clues. Interoceptive cues are includedin those provided by “Other Sense Organs” of FIG. 1B. However, in thepresent context we refer not to such naturally occurring interoceptivesignals, but instead to interoceptive signals that are producedartificially as a result of the vagus nerve stimulation. They correspondto the stimulation of afferent vagus nerve fibers that convey a sense oftheir excitation to regions of the brain that could result in theconscious but artificial awareness of the viscera, particularly theanterior insula (see FIG. 12) [CRITCHLEY H D, Wiens S, Rotshtein P,Ohman A, Dolan R J. Neural systems supporting interoceptive awareness.Nat Neurosci 7(2,2004):189-195; CRAIG, A. D. How do you feel?Introception: the sense of the physiological condition of the body. Nat.Rev. Neurosci 3(2002):655-666; CRAIG A D. How do you feel—now? Theanterior insula and human awareness. Nat Rev Neurosci 10(1,2009):59-70].In one embodiment, the magnitude of stimulation of those afferent fibersis made to increase or decrease according to the corresponding level ofthe physiological signal that is being sensed. One may regard thatmethod as a type of augmented biofeedback that involves interoceptivesensation, rather than exteroceptive sensation. This stimulation ofafferent vagal nerve fibers is also intended to simulate the adaptationof interoceptors that may be required for the direct, voluntary controlof the viscera [Barry R. DWORKIN. Learning and Physiological Regulation.Chicago: University of Chicago Press, 1993, Chapter 8, pp. 162-185].

After determining whether and to what extent the patient is able toconsciously control the biofeedback signal, biofeedback will besuspended and the parameters suitable for vagus nerve stimulation willthen be determined. Ordinarily, the amplitude of the stimulation signalis set to the maximum that is comfortable for the patient, and then theother stimulation parameters are adjusted. In general, the stimulatorsignal may have a frequency and other parameters that are selected toproduce a therapeutic result in the patient, i.e., stimulationparameters for each patient are adjusted on an individualized basis, inorder to produce an effect that is relevant to the condition that isbeing treated. The parameter values may be selected in such a way as toactivate or suppress particular resting state networks of the brain thatare relevant to the patient's condition, as described in the sectionabove entitled “Selection of stimulation parameters to activate orsuppress selected resting state networks of the brain.” Preliminarycontrol theory procedures, including tuning and the training of asupport vector machine, may also be performed in order to allow thesystem to vary its stimulation parameters in response to fluctuatingenvironmental and sensed physiological signals, as described in thesection “Use of biofeedback and automatic control theory methods totreat and train patients.”

A typical stimulation waveform was shown in FIGS. 11B and 11C. As seenthere, individual sinusoidal pulses have a period of tau, and a burstconsists of N such pulses. This is followed by a period with no signal(the inter-burst period). The pattern of a burst followed by silentinter-burst period repeats itself with a period of T. For example, thesinusoidal period tau may be 200 microseconds; the number of pulses perburst may be N=5; and the whole pattern of burst followed by silentinter-burst period may have a period of T=40000 microseconds, which iscomparable to 25 Hz stimulation. More generally, there may be 1 to 20pulses per burst, preferably five pulses. Each pulse within a burst hasa duration of 1 to 1000 microseconds (i.e., about 1 to 10 KHz),preferably 200 microseconds (about 5 KHz). A burst followed by a silentinter-burst interval repeats at 1 to 5000 bursts per second (bps),preferably at 5-50 bps, and even more preferably 10-25 bps stimulation(10-25 Hz). The preferred shape of each pulse is a full sinusoidal wave,although triangular or other shapes may be used as well.

Such a signal may be constructed by circuits within the stimulatorhousing (30 in FIG. 3), or it may be transmitted to the housing usingradio transmission from the base station or any of the other componentsof the control unit (see FIG. 6). Compression of the signal is alsopossible, by transmitting only the signal parameters tau, N, T, Emax,etc., but in that case, the stimulator housing's control electronicswould then have to construct the waveform from the transmittedparameters.

After the cutaneous and deep nerve stimulation waveform parameters havebeen preliminarily selected, and it has been determined that the patientcan perform biofeedback, stimulation sessions can be initiated in whichthe biofeedback and vagus nerve stimulation are performedsimultaneously. The duration of a stimulation session depends on thephysiological condition that is being treated, and success of thestimulation may be judged in terms of whether the sensed physiologicalsignal is adjusted by the stimulation to be within a clinicallydesirable range. Alternatively, other indices of clinical success may bemade, depending on the condition that is being treated.

The three mechanisms shown in FIG. 1B (biofeedback, artificialinteroceptive sensation, and direct stimulation via the vagus nerve toeffect automatic control) will collectively modulate the physiologicalsystem, interacting with one another to determine the value of thesensed physiological signal. Part of the interaction is determined bythe manner in which the nerve stimulator/biofeedbackdevice/physiological controller is programmed. For example, directstimulation of the physiological system via the vagus nerve may beprogrammed to follow and amplify changes that occur as a result ofbiofeedback. An embodiment of that example would occur when a migraineuruses galvanic skin response biofeedback alone to consciously reducesympathetic tone through muscular and emotional modulation, whereuponthe device senses that reduction through its programming and thenamplifies the effect by increasing parasympathetic tone after a brieftime delay, by directly stimulating vagal parasympathetic efferent nervefibers. The present invention may be used to amplify suchbiofeedback-induced effects by first detecting the patient's attemptedmuscular relaxation and the associated reduction in sympathetic tone,and by then stimulating the vagus nerve to increase parasympathetictone.

In migraine patients, biofeedback may also involve an attempt tomodulate components of evoked potentials that are related to aparticular pathway, generally by decreasing the magnitude of particularpeak or troughs that may be associated with pain. The migraine-relatedpathway involves pre- and postganglionic parasympathetic neurons in thesuperior salivatory nucleus (SSN) and sphenopalatine ganglion (SPG),respectively. The SSN stimulates the release of acetylcholine,vasopressin intestinal peptide, and nitric oxide from meningealterminals of SPG neurons, resulting directly or indirectly in themigraine-related cascade of events that include the dilation ofintracranial blood vessels, plasma protein extravasation, and localrelease of inflammatory molecules that activate adjacent terminals ofmeningeal nociceptors. The SSN receives extensive input from more thanfifty brain areas, many of which may be modulated by the locus ceruleus.

When the locus ceruleus is activated through vagus nerve stimulation, itwill respond by increasing norepinephrine secretion, which in turn willalter cognitive function through the prefrontal cortex, increasemotivation through nucleus accumbens, activate thehypothalamic-pituitary-adrenal axis, and increase the sympatheticdischarge/inhibit parasympathetic tone through the brainstem. Suchinhibition of parasympathetic tone will specifically inhibit theparasympathetic pathway via the superior salivatory nucleus, therebyblocking the positive feedback loop that contributes to the maintenanceof migraine pain [Commonly assigned, co-pending patent applicationUS20110276107, entitled Electrical and magnetic stimulators used totreat migraine/sinus headache, rhinitis, sinusitis, rhinosinusitis, andcomorbid disorders, to SIMON et al, which is hereby incorporated byreference].

Minimally Invasive Embodiment of the Vagus Nerve Stimulator

An alternate embodiment of the present invention, involving minimallyinvasive rather than noninvasive vagus nerve stimulation, is illustratedby FIG. 15. As ordinarily practiced, the electrodes used to stimulate avagus nerve are implanted about the nerve during open neck surgery.However, in a commonly assigned, copending application, Applicantdisclosed that it is also possible to electrically stimulate a vagusnerve using a minimally invasive surgical approach, namely percutaneousnerve stimulation. In that procedure, a pair of electrodes (an activeand a return electrode) are introduced through the skin of a patient'sneck to the vicinity of a vagus nerve, and wires connected to theelectrodes extend out of the patient's skin to a pulse generator[Publication number US20100241188, entitled Percutaneous electricaltreatment of tissue, to J. P. ERRICO et al.; SEPULVEDA P, Bohill G,Hoffmann T J. Treatment of asthmatic bronchoconstriction by percutaneouslow voltage vagal nerve stimulation: case report. Internet J AsthmaAllergy Immunol 7(2009):e1 (pp 1-6); MINER, J. R., Lewis, L. M.,Mosnaim, G. S., Varon, J., Theodoro, D. Hoffman, T. J. Feasibility ofpercutaneous vagus nerve stimulation for the treatment of acute asthmaexacerbations. Acad Emerg Med 2012; 19: 421-429].

In the present invention, electrodes are preferably also introducedpercutaneously to the vicinity of a vagus nerve, but unlike the previousminimally invasive disclosure, the electrodes are not ultimatelyconnected to wires that extend outside the patient's skin. Instead, inthe present invention, the percutaneously implanted stimulator receivesenergy wirelessly from an external transmitter that need not be in closeproximity to the skin of the patient, and electrical pulse generationoccurs within the implanted stimulator using that energy.

As shown in FIG. 15A, the nerve modulating device 300 of the minimallyinvasive embodiment of the invention (also known as an implantable leadmodule or simply an electrical nerve stimulator) is powered by thereceipt of far-field or approximately plane wave electromagnetic energywith frequencies in the range of 0.3 to 10 GHz (preferably about 800 MHzto about 6 GHz, and more preferably about 800 MHz to about 1.2 MHz)which is received wirelessly by an antenna 360 within, or attached to,the device 300. The energy that powers the nerve modulating device 300is transmitted by an external device, which in FIG. 15A is labeled as aController 370. Controller 370 is in turn controlled by a programmerdevice 380, which preferably communicates with controller 370wirelessly. In operation, the nerve modulating device 300 is implantedwithin the patient, the controller 370 may be either outside of thepatient or implanted within the patient, and the programmer 380 isoperated manually by the patient or a caregiver. The antenna of thecontroller 370 is actively tuned/matched to the resonant frequency of anantenna in the implanted device 300 so that the maximum efficiency ofpower transmission is achieved. There may be several antennae at variousorientations in the external unit and/or in the implanted signalgenerator to enhance coupling efficiency in various orientations. Theunit 370 supplying power and control to the implanted device 300 couldbe AC powered and/or battery powered. If powered by rechargeablebatteries, a battery charger may be an accessory to the system. Thecontroller 370 is preferably both portable and rechargeable. In oneembodiment, it may be worn around the neck as a pendant, placed in apocket, or clipped to clothing. This wireless transmitter 370 ispreferably recharged at a recharging base and has a significant range oftransmission, preferably up to four feet, so that patients can sleepwithout having to wear the transmitter.

FIG. 15B is a more detailed schematic diagram of the nerve modulatingdevice 300 for delivering electrical impulses to nerves. As shown,device 300 comprises an electrical impulse generator 310; a power source320 coupled to the electrical impulse generator 310; a control unit 330in communication with the electrical impulse generator 310 and coupledto the power source 320; and one or more electrodes 340 coupled to theelectrical impulse generator 310. Nerve modulating device 300 isconfigured to generate electrical impulses sufficient to modulate theactivity of one or more selected regions of a nerve (not shown). Thepower source 320 receives energy wirelessly via an antenna 360, whereinthe energy is in the form of far-field or approximately plane-waveelectromagnetic waves with frequencies in the range of 0.3 to 10 GHz,preferably about 800 MHz to about 1.2 MHz.

The control unit 330 may control the electrical impulse generator 310for generation of a signal suitable for amelioration of a patient'scondition when the signal is applied via the electrodes 340 to thenerve. It is noted that nerve modulating device 300 excluding theelectrodes 340 may be referred to by its function as a pulse generator.U.S. Patent Application Publications 2005/0075701 and 2005/0075702, bothto SHAFER, both of which are incorporated herein by reference, relatingto stimulation of neurons of the sympathetic nervous system to attenuatean immune response, contain descriptions of pulse generators that may beapplicable to various embodiments of the present invention.

FIG. 15C illustrates one embodiment of the nerve modulating device 300that consumes relatively little power and may therefore receive powerfrom a correspondingly weak and/or distant external transmitter. Toachieve low power consumption, the embodiment is designed to use aminimum of components. This may be accomplished by designing the deviceto produce constant voltage pulses, rather than constant current pulses,because circuits for the latter are more complex and consume more powerthan the former. However, for some patients a constant current pulse maybe preferred, depending on the detailed anatomy of the patient's neck inthe vicinity of the stimulated nerve (see below). Consequently, constantcurrent pulses are also contemplated by the invention [DELIMA, J. A. andCordeiro, A. S. A simple constant-current neural stimulator withaccurate pulse-amplitude control. Engineering in Medicine and BiologySociety, 2001. Proceedings of the 23rd Annual International Conferenceof the IEEE (Vol. 2, 2001) 1328-1331]. In either case, simplicity ofcircuit design is provided by a design that makes the amplitude of thepulse constant, rather than by allowing the amplitude to be variable.Accordingly, the present invention modulates the stimulation power tothe nerve by altering the number and timing of the pulses, rather thanby modulating the amplitude of individual pulses. Additional simplicityof design may be achieved by using communication that occurs in onedirection only, from the transmitter to the stimulator (simplexcommunication according to the ANSI definition, rather than half or fullduplex communication).

The stimulator circuit is novel in that it removes one (or more)elements from conventional stimulators, without sacrificing performance.In particular, the present invention removes from conventional designsthe ability of the stimulator to vary the amplitude of the stimulationpulses. Unexpectedly, one can get substantially the same stimulatoryeffect as that provided by conventional stimulators, by keeping waveformparameters fixed, particularly the amplitude of pulses, but by thencontrolling the number and timing of pulses that the nerve experiences,in order to achieve the same physiologically desirable level of nervestimulation. In essence, this invention uses an adjustable number offixed voltage (or fixed current) pulses with fixed duration to elicitdesired changes in nerve response. These fixed voltage pulses create onelong continuous pulse to the nerve to ensure that sufficient energy isdelivered to the nerve to cause the nerve to reach its action potentialand fire. Thus, the present invention reaches the threshold energy levelfor a nerve to fire by adjusting the duration of the pulse received bythe nerve, rather than adjusting the amplitude of the pulse.

In another aspect of the invention, the specific number of fixedamplitude pulses that will be delivered to the nerve is preferablydetermined through an iterative process with each patient. Once thesurgeon determines the number of fixed voltage pulses required tostimulate the nerve for a particular patient, this number is programmedinto either the external controller or the implantable stimulator.

A constant-voltage pulse design teaches against prevailing preferreddesigns for vagus nerve stimulators. Thus, constant-voltage pulses areused in cardiac pacemakers, deep brain stimulation, and some implantableneuromodulators for treatment of incontinence and chronic pain, butconstant-current pulses are used for cochlear implants and vagus nervestimulators [D. PRUTCHI and M. Norris Stimulation of excitable tissues.Chapter 7, pp. 305-368. In: Design and development of medical electronicinstrumentation. Hoboken: John Wiley & Sons, 2005]. In the latterapplications, the constant current design is said to be preferredbecause slight variations in stimulator-to-nerve distance change theability of the constant-voltage pulse stimulator to depolarize thenerve, which is less of a problem with constant-current pulsestimulators. With the constant current design, the stimulationthresholds stay more or less constant even with changing electrodeimpedance and ingrowth of tissue into the neural interface [Emarit RANU.Electronics. Chapter 10, pp. 213-243. In: Jeffrey E. Arle, Jay L. Shils(eds). Essential Neuromodulation. Amsterdam, Boston: Academic Press.2011]. For example, the BION stimulators described in the backgroundsection of the present application generate only constant currentpulses.

In some embodiments of the present invention, a constant voltage pulseis used because it can be produced with a simpler circuit that consumesless power, as compared with constant pulse current circuits. Theabove-mentioned potential problem with variation in stimulator-to-nervedistance is addressed by anchoring the stimulator to the vagus nerve.Furthermore, the problem may be circumvented to some extent in thepresent invention by coating the stimulator's electrodes with a verythin layer of poorly conducting material. This is because the presenceof a poorly conducting boundary layer surrounding the stimulatorminimizes the differential effects of conductivity variations andelectrode location during constant current and constant voltagestimulation [Mark M. STECKER. Nerve stimulation with an electrode offinite size: differences between constant current and constant voltagestimulation. Computers in Biology and Medicine 34(2004):51-94].

Additional circuit simplicity and minimized power requirements areaccomplished in the embodiment shown in FIG. 15C by fixing thecharacteristics of the stimulation pulses, rather than by addingcircuits that would allow the characteristics to be adjusted through useof external control signals. For example, the output pulses shown inFIG. 15C are shown to be generated using a pair of monostablemultivibrators. The first multivibrator receives a trigger pulse fromthe control unit 330, resulting in a pulse of fixed duration. The secondmultivibrator is triggered by the falling edge of the firstmultivibrator's pulse, and the pair of pulses from the twomultivibrators are combined with suitable polarity using a differentialoperational amplifier. Thus, in this example, the impulse generator 310consists of the multivibrators and operational amplifier. The amplifierin turn presents the stimulation pulses to the electrodes 340. The timeperiod that a monostable multivibrator remains in its unstable state(the pulse width) is a function of its component resistor and capacitorvalues, so if the pulse width can be preselected for a patient, thedevice can be designed using correspondingly fixed R and C values. Onthe other hand, if a variable pulse width is needed during preliminarytesting with a patient, the multivibrator circuit can be made morecomplex, with the pulse width selected on the basis of coded signalsthat are transmitted to the impulse generator 310 via the control unit330. Once the appropriate pulse width has been selected, a controlsignal may be sent from the control unit 330 to disable extraneous powerconsumption by the variable pulse-width circuitry. Proper pulse width isparticularly important in stimulating nerve fibers having theappropriate diameters [see discussion below and SZLAVIK R B, de Bruin H.The effect of stimulus current pulse width on nerve fiber sizerecruitment patterns. Med Eng Phys 21(6-7,1999):507-515].

It is also understood that more complex pulses may also be preferred,which would require a correspondingly more complex circuitry andpossibly additional power consumption, as compared with the circuitshown in FIG. 15C [JEZERNIK S, Morari M. Energy-optimal electricalexcitation of nerve fibers. IEEE Trans Biomed Eng 52(4,2005):740-743;Wongsarnpigoon A, Woock J P, Grill W M. Efficiency analysis of waveformshape for electrical excitation of nerve fibers. IEEE Trans Neural SystRehabil Eng 18(3,2010):319-328; FOUTZ T J, Ackermann D M Jr, Kilgore KL, McIntyre C C (2012) Energy efficient neural stimulation: couplingcircuit design and membrane biophysics. PLoSONE 7(12): e51901.doi:10.1371/journal.pone.0051901, pp. 1-8; McLEOD K J, Lovely D F, ScottR N. A biphasic pulse burst generator for afferent nerve stimulation.Med Biol Eng Comput 25(1,1987):77-80].

The control unit 330 in FIG. 15C is shown to exercise its control onlyby presenting trigger pulses to the impulse generator 310. In thisexample, the train of pulses appearing across the electrodes 340 isdetermined only by the timing of the sequence of trigger pulses. Thetrigger pulses are themselves encoded in the signal that is transmittedfrom controller 370 in FIG. 15A, shown in FIG. 15C as “RF signal withencoded trigger pulse.” The trigger pulses are extracted andreconstructed from the transmitted signal by an RF demodulator in thecontrol unit 330. There are many methods for transmitting and decodingsuch control signals, and the present invention may be designed to useany of them [Robert PUERS and Jef Thoné. Short distance wirelesscommunications. Chapter 7, pp. 219-277, In: H.-J. Yoo, C. van Hoof(eds.), Bio-Medical CMOS ICs. New York: Springer, 2011]. Because thetiming of pulses is determined by the trigger pulses emanating from thetransmitted signal, the circuit shown in FIG. 15C does not even need aclock, thereby reducing its power requirements. However, in otherembodiments a clock may be included as part of the timing circuitry. Itis understood that in order to command a pulse of the treatment signaland switch that pulse to the electrodes, it is possible to use a controlRF signal having a different frequency than the one used to providepower, or encode the command based on variation in the RF signal'samplitude, pulse width and/or duration.

The transmitted RF signal is received by an antenna 360, and the signalprovides power for the stimulation device 300, in addition to thecontrol signals. The power is provided by the power source 320 in FIG.15C. As shown there, energy from the transmitted RF signal (beamedpower) is accumulated in a storage capacitor, which is eventuallydischarged in conjunction with the creation of stimulation pulses thatare applied to the electrodes 340. In addition to the beamed power,there may also be scavenged power, which arises from the reception ofambient electromagnetic radiation by the antenna 360. Special circuitsand antennas may be used to scavenge such ambient electromagneticradiation [Soheil RADIOM, Majid Baghaei-Nejad, Guy Vandenbosch, Li-RongZheng, Georges Gielen. Far-field RF Powering System for RFID andImplantable Devices with Monolithically Integrated On-Chip Antenna. In:Proc. Radio Frequency Integrated Circuits Symposium (RFIC), 2010 IEEE,Anaheim, Calif., 23-25 May 2010, pp. 113-116]. Power scavenging may bemost appropriate in a hospital setting where there is significantambient electromagnetic radiation, due to the use there of diathermyunits and the like [FLODERUS B, Stenlund C, Carlgren F. Occupationalexposures to high frequency electromagnetic fields in the intermediaterange (>300 Hz-10 MHz). Bioelectromagnetics 23(8,2002):568-577].

The stimulator circuit comprises either a battery or a storage device,such as a capacitor, for storing energy or charge and then deliveringthat charge to the circuit to enable the circuit to generate theelectrical impulses and deliver those impulses to the electrodes. Theenergy for the storage device is preferably wirelessly transmitted tothe stimulator circuit through a carrier signal from the externalcontroller. In the preferred embodiments, the energy is delivered to theenergy storage device between electrical impulses. Thus, the energy isnot being delivered in “real-time”, but during the periods when thepulse is not being delivered to the nerve or during the refractoryperiod of the nerve. For example, a typical electrical impulse may be ONfor about 200 uS and then OFF for about 39,000 uS. The energy isdelivered during this longer OFF time, which enables the system to use amuch smaller signal from the external generator. The external generatordelivers the carrier signal over the OFF period to charge the energystorage device, which then releases this energy or charge to theremainder of the circuit to deliver the electrical impulse during the200 uS ON time.

Transmitting energy to the storage device in between the electricalimpulses provides a number of advantages. First, it increases the lengthof time that the electrical energy can be delivered to charge thestorage device. This reduces the strength of the signal required todeliver the electrical energy to the storage device, thereby reducingthe overall power requirements of the external controller and reducingthe complexity of the stimulator circuitry. In addition, it enhances thesafety of the device because it reduces the risk that uncontrolledenvironmental RF energy will create an electrical connection between thenerve and the charged energy. Since the storage device is receivingelectrical energy between electrical impulses, there is no electricalconnection between the stimulator circuit and the nerve as the storagedevice is charged. This reduces the risk of the electrical energy beingaccidently applied to the nerve.

In order to power the impulse generator and demodulation circuits, thepower source 320 in FIG. 15C makes use of a voltage regulator, theoutput from which is a stable voltage V. The circuits that may beselected for the voltage regulator comprise those described by BOYLESTAD[Robert L BOYLESTAD and Louis Nashelsky. Power Supplies (VoltageRegulators). Chapter 18, pp. 859-888. In: Electronic devices and circuittheory, 8th ed. Upper Saddle River, N.J.: Prentice Hall, 2002].

In preferred embodiments of the minimally invasive stimulator, theparameters of fixed stimulation pulses are generally as follows. Theshape of the pulse is square, sine, triangular or trapezoidal withnegative voltage return to eliminate DC bias. The electrical impulsewill typically have a frequency of between about 1-500 Hz, preferablyabout 1 to 50 Hz, and more preferably about 10-35 Hz. In an exemplaryembodiment, the frequency for the impulse received by the nerve is about25 Hz. The preferred fixed voltage received by the nerve is betweenabout 1-20 V and will typically vary depending on the size and type ofelectrode and the distance between the electrode and the nerve. Incertain embodiments where the nerve is directly attached to the nerve(or implanted adjacent to the nerve), the fixed voltage is preferablyabout 1 to 4 volts, more preferably about 2 volts. In other embodiments,wherein the electrode is, for example, injected into the patient andimplanted outside of the sheath, the voltage is preferably between about7-15 volts and more preferably about 10 V. In embodiments wherein thecurrent is fixed or held constant, the preferred fixed current is about0.5 mA to about 20 mA. Similar to voltage, the fixed current will varydepending on the size and type of electrode and its distance from thenerve. In those embodiments where the electrode is adjacent to, or on,the nerve, the current is preferably about 0.5 to 5 mA and morepreferably about 3.5 mA. In those embodiments, where the electrode isspaced from the nerve (just as an injectable electrode outside of thesheath), the current is preferably about 7-15 mA and more preferablyabout 10 mA. The pulse duration is preferably between about 50 to 1000uS.

Benefits of the disclosed system include the following features. Theimplanted signal generator can be much smaller than a traditionalimplanted generator. The surgery to implant this system can be doneunder local anesthesia on an outpatient basis in a non-hospital settingresulting in faster recovery and less scarring. Furthermore, since thereis no implanted battery, the patient does not need additional surgeriesto replace batteries, which is especially important if the patient has atreatment protocol that requires treatments involving significant powerand duration. Also, the limited circuitry implanted in the body will bemore reliable than traditional implanted generators. Because thetreatment is powered and controlled from outside the body, changes tothe treatment protocol can be made quickly and easily. In the event ofan emergency, the patient or caregiver can quickly turn-off or removethe power/control unit to stop treatment.

The stimulator circuit is novel in that it removes one (or more)elements from conventional stimulators, without sacrificing performance.In particular, the present invention removes from conventional designsthe ability of the stimulator to vary the amplitude of the stimulationpulses. Unexpectedly, one can get substantially the same stimulatoryeffect as that provided by conventional stimulators, by keeping waveformparameters fixed, particularly the amplitude of pulses, but by thencontrolling the number and timing of pulses that the nerve experiences,in order to achieve the same physiologically desirable level of nervestimulation. In essence, this invention is using an adjustable number offixed voltage (or current) pulses with fixed duration to elicit desiredchanges in nerve response.

The electrode and signal generator are primarily, but not exclusively,intended for stimulation of the vagus nerve in the neck, for conditionsthat include headache and fibromyalgia. In those applications, thetypical signal would be square or sine pulses of fixed amplitudeapproximately 2 Volts, where each pulse has a fixed duration of 200 uS.Typically 5 of these pulses would be produced every 40 mS to produce aneffective 25 Hz signal.

Although the preferred embodiments of the invention are as describedabove, it is understood that one may also modify the capabilities of thedevice as follows. Optionally, the pulse command could have an addressor other identifier associated with it so that only a particular signalgenerator would be activated. This would allow a patient to havemultiple implanted signal generators in the body with each responding toits own command from the same or multiple power/control units. Anotheroption would be to have circuitry or a processor in the implanted signalgenerator that could communicate a signal back to the power/controlunit. This signal could contain status information such as voltage,current, number of pulses applied or other applicable data. The antennaeand RF signals in this system could also be replaced by closely coupledcoils of wire and lower frequency signals that are inductively coupledthrough the body.

For such minimally invasive stimulators, the cutaneous (e.g. tactile)stimulation shown in FIG. 1B is not feasible unless additionalskin-surface electrodes were to be applied to the subject. Nevertheless,in such applications, the individual may also consciously respond to theartificial interoceptive signals that are applied through the minimallyinvasive vagus nerve stimulator, as though they were a biofeedbacksignal. Otherwise, the biofeedback methods that are disclosed hereinwould have to be performed using sensory modalities that do not involvecervical electrical stimulation, for example, by using auditory orvisual biofeedback that is produced through the “Other Sensory Stimuli”component of FIG. 1B.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method for treating a medical conditionin a patient, the method comprising: applying a first sensory stimulusto the patient; measuring a first baseline evoked potential from thepatient, wherein the first baseline potential is evoked by the firstsensory stimulus; applying an electrical impulse transcutaneouslythrough an outer skin surface of the patient to a vagus nerve of thepatient; measuring a second evoked potential from the patient subsequentto the applying, wherein the second evoked potential relates to aresponse of the patient to the medical condition as a function of acharacteristic of the electrical impulse; comparing a characteristic ofthe first baseline evoked potential with a characteristic of the secondevoked potential; and determining, based on the comparing, whether theelectrical impulse has triggered an action potential in the vagus nerve.2. The method of claim 1, further comprising: varying an amplitude ofthe electrical impulse based on the comparing.
 3. The method of claim 1,further comprising: varying a frequency of the electrical impulse basedon the comparing.
 4. The method of claim 1, wherein the applyingcomprises positioning an electrode in contact with the outer skinsurface.
 5. The method of claim 4, further comprising: varying aposition of the electrode on the outer skin surface based on thecomparing.
 6. The method of claim 4, further comprising: varying anorientation of the electrode on the outer skin surface based on thecomparing.
 7. The method of claim 1, wherein the measuring comprisespositioning an electrode on a scalp of the patient and measuring avoltage fluctuation arising from an ionic current within a brain of thepatient.
 8. The method of claim 1, further comprising: measuring anacute response of the patient to the medical condition as a function ofa characteristic of the electrical impulse; and comparing the acuteresponse with the first baseline evoked potential and the second evokedpotential.
 9. The method of claim 8, wherein the acute responsecomprises a reduction in pain.
 10. The method of claim 1, wherein thesensory stimulus comprises at least one of a visual stimulus, anauditory stimulus, a somatosensory stimulus, a painful stimulus, anolfactory stimulus, a gustatory stimulus, a vestibular stimulus, or aninteroceptive stimulus.
 11. The method of claim 1, wherein the actionpotential in the vagus nerve is associated with an increase in ahabituation of the second evoked potential compared to a habituation ofthe first baseline evoked potential.
 12. The method of claim 1, whereinthe action potential in the vagus nerve is associated with a deficit ina habituation of the second evoked potential compared to a habituationof the first baseline evoked potential.
 13. The method of claim 1,wherein the medical condition comprises a primary headache.
 14. A methodfor treating a medical condition in a patient, the method comprising:applying a first sensory stimulus to the patient; measuring a firstbaseline electrical potential from the patient, wherein the firstbaseline electrical potential is evoked by the first sensory stimulus;applying an electrical impulse transcutaneously through an outer skinsurface of a neck of the patient to a vagus nerve of the patient;measuring an acute response of the patient to the medical condition as afunction of a characteristic of the electrical impulse; and comparingthe acute response with the first baseline electrical potential.
 15. Themethod of claim 14, further comprising varying an amplitude of theelectrical impulse based on the comparing.
 16. The method of claim 14further comprising varying a frequency of the electrical impulse basedon the comparing.
 17. The method of claim 14 wherein the applyingcomprises positioning an electrode in contact with the outer skinsurface.
 18. The method of claim 17 further comprising varying aposition of the electrode on the outer skin surface based on thecomparing.
 19. The method of claim 17 further comprising varying anorientation of the electrode on the outer skin surface based on thecomparing.
 20. The method of claim 14 wherein the first sensory stimuluscomprises at least one of a visual stimulus, an auditory stimulus, asomatosensory stimulus, a painful stimulus, an olfactory stimulus, agustatory stimulus, a vestibular stimulus, or an interoceptive stimulus.21. The method of claim 14 further comprising determining, based on thecomparing, whether the electrical impulse has triggered an actionpotential in the vagus nerve.
 22. The method of claim 21 wherein theaction potential in the vagus nerve is associated with an increase in ahabituation of the acute response compared to a habituation of the firstbaseline electrical potential.
 23. The method of claim 21 wherein theaction potential in the vagus nerve is associated with a deficit in ahabituation of the acute response compared to a habituation of the firstbaseline electrical potential.
 24. The method of claim 14 wherein themedical condition comprises a primary headache.
 25. The method of claim24 wherein the acute response is a reduction in pain.
 26. A methodcomprising: measuring a first evoked potential from a patient having anouter skin surface and a vagus nerve, wherein the first evoked potentialhas a first characteristic and was evoked via a first sensory stimulusapplied to the patient; applying an electrical impulse transcutaneouslythrough the outer skin surface to the vagus nerve after the first evokedpotential has been measured; measuring a second evoked potential fromthe patient responsive to the electrical impulse being applied, whereinthe second evoked potential has a second characteristic, performing acomparison between the first characteristic and the secondcharacteristic; and taking an action based on the comparison beinginformative of the electrical impulse causing a response in the patient.27. The method of claim 26, wherein the electrical impulse causes anaction potential in the vagus nerve.